It should say so on the packaging it came in.
A "Proof FDC" coin is struck with a specially prepared and highly polished die and the flat surfaces of the coin have a mirror like finish.
A "Frosted" coin is a Proof FDC coin that has the raised parts of the design sandblasted of treated with acid to give a "Matt" appearance and make the raised design stand out against the mirror like finish of the flat surfaces.
The extra work put into a Proof coin is reflected in the price you pay for it. They are always significantly more expensive than regular uncirculated or specimen coins.
Pictures of a specific coin are difficult to come by. The coin shown in the related link below shows a "Proof" coin.
A British 1970 Shilling (English reverse) (Proof FDC), uncirculated and in absolute mint condition could fetch up to £3 GBP. A British 1970 Shilling (Scottish reverse) (Proof FDC), uncirculated and in absolute mint condition could fetch up to £2 GBP. A reputable coin dealer will be able to give a more accurate valuation.
From 1816 to 1919 inclusive, British Shillings were minted from 0.925 fine silver. The only exception to this was a Proof in gold FDC Shilling in 1816 which is so rare it is unlikely to exist outside of a museum. If you do have a gold 1860 Shilling, it is because somebody has plated it, rendering it worthless as a collectible.
A British 1883 sterling silver Shilling (Victoria), uncirculated and in absolute mint condition could fetch up to £200 GBP. If it has been circulated but still in good condition, it might fetch anything from £10 to £90 GBP. A British 1883 sterling silver Shilling (Victoria)(Proof FDC - plain edge), uncirculated and in absolute mint condition could fetch up to £3,750 GBP. NOTE - The reverse of these coins is upside down to the obverse. This is normal. The values quoted are the best possible for the best specimens in their grades, but may be significantly lower due to varying demand for the coin and the prevailing economic climate. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coin.
A British 1829 Shilling, uncirculated and in absolute mint condition could fetch up to £550 GBP. If it has been circulated but still in good condition, it might fetch anything from £30 to £225 GBP. A British 1829 Shilling (Proof FDC), uncirculated and in absolute mint condition could fetch up to £2,250 GBP. A reputable coin dealer will be able to give a more accurate valuation.
A British 1821 Shilling, uncirculated and in absolute mint condition could fetch up to £350 GBP. If it has been circulated but still in good condition, it might fetch anything from £10 to £140 GBP. A British 1821 Shilling (Proof FDC), uncirculated and in absolute mint condition could fetch up to £850 GBP. A reputable coin dealer will be able to give a more accurate valuation.
KG VI means King George VI. A "Matt Proof" coin is a process where the surface of the coin is deliberately finely granulated as distinct from the usual mirror like surface of "Proof" coins with frosted highlights. The flat surfaces will have a satin like appearance. FDC is an abbreviation for Fleur du Coin. It refers to a "Proof" coin that has been hand finished.
A frosted proof coins were issued by the US Mint prior to 1936. In appearance they have a mirrorlike field [[the field of a coin is the flat areas not covered by the design]]with the design of the coin appearing to be frosted or dull in comparison to the field. This type of proof was again used on proof coins in the late 1970s and are refered to as "cameo" proofs. A mirror proof [[also called a Brilliant Proof]] has a mirrorlike surface over the entire coin. This type of proof was issued by the Mint from 1936 until sometime in the late 1970s.
The 1927 British Florin (Two Shillings) was not issued as a general circulation coin, it was only released as a "Proof FDC" and a "Matt Proof FDC" coin and there were only 15,000 minted. The Matt Proof FDC coin is described as being of the highest rarity. The Proof FDC coin would perhaps be described as being scarce.
A "Proof" or "Proof - Fleur Du Coin" coin is one that is struck on specially prepared and highly polished dies. After the coin is struck, it is hand polished to give a mirror like finish. Most modern "Proof" coins have the highlights frosted to give a good contrast. "Proof" coins are made from the same metal as general circulation coins, but are often also made from silver or gold. "Proof" coins are worth a good deal more than their face value and are intended as a souvenir or investment.
There was only one type of 1953 British Crown minted, but it had three different finishes. The general circulation coin appears much as you would expect. The "Frosted VIP Proof" coin will have frosted highlights. The raised areas will be slightly dulled by sandblasting or etching of the die. The "Matt Proof FDC" coin is sufficiently rare that identifying one will not be an issue. The flat surfaces which are usually shiny, will be finely granulated.
A "Matt Proof" coin is a process where the surface of the coin is deliberately finely granulated as distinct from the usual mirror like surface of "Proof" coins with frosted highlights. The flat surfaces will have a satin like appearance. FDC is an abbreviation for Fleur du Coin. It refers to a "Proof" coin that has been hand finished. Any such coins are usually protectively packaged by the Mint and are sold at a price well above the face value of the coin.
A British 1787 silver Shilling (George III)(No semee of hearts in Hanoverian shield on reverse), circulated but still in good condition, might fetch anything from £22 to £110 GBP. A British 1787 silver Shilling (George III)(Proof FDC)(No semee of hearts in Hanoverian shield on reverse) is considered to be extremely rare. A British 1787 silver Shilling (George III)(Plain edge - Proof FDC)(No semee of hearts in Hanoverian shield on reverse) is considered to be extremely rare. A British 1787 silver Shilling (George III)(no stop over head), circulated but still in good condition, might fetch anything from £35 to £175 GBP. A British 1787 silver Shilling (George III)(no stops at date), circulated but still in good condition, might fetch anything from £45 to £250 GBP. A British 1787 silver Shilling (George III)(no stops on obverse), circulated but still in good condition, might fetch anything from £275 to £1,750 GBP. A British 1787 silver Shilling (George III)(with semee of hearts on reverse), circulated but still in good condition, might fetch anything from £25 to £100 GBP. A British 1787 silver Shilling (George III)(1/1 retrograde)(with semee of hearts on reverse), circulated but still in good condition, might fetch anything from £45 to £300 GBP. A British 1787 silver Shilling (George III)(plain edge Proof FDC)(with semee of hearts on reverse) is considered to be extremely rare. The values quoted are the best possible for the best specimens in their grades, but may be significantly lower due to varying demand for the coin and the prevailing economic climate. A reputable coin dealer will be able to give a more accurate valuation based on inspection of the coin.