You would have to research the acient times to find out, or wait for answers...;)
Polonium got is symbol (Po) from the first two letters of its name. Polonium was named after the nation of Poland by its discoverers Marie and Pierre Curie.
The name of the element with symbol 'He' is Helium. It has got 2 Protons and two neutrons in the nucleus and 2 electrons moving around it. It is first in the series of 'Nobel' gases. Others being Neon, Argon, Krypton,Xenon and Radon.
Some of them got their symbol from their Latin name.
Atomic MassAtomic NumberSymbol
Fe is Iron. It isn't 'Ir' because they got Fe from iron's Latin name, ferum. It also can't be 'Ir' because Ir is already the symbol for another element, iridium.
Lithium got its chemical symbol from the first two letters of its name.
Silver, symbol Ag, is for argentum, which is "silver" in Latin See the Related Questions link for how the elements got their names and symbols.
Dimitri Mendeleev predicted this element and named dvi-tellurium; Curie called the new element polonium with the chemical symbol Po. Some polonium isotopes had during the time different names today obsolete.
Plutonium chemical symbol is formed from the first and third letters of name - Pu.
The name of the chemical element neptunium is derived from the name pf the planet Neptune.And Neptune was the got of seas in the Roman mythology.
The name of the chemical element is derived from the name of the planet Uranus.This name was chosen by Klaproth.
While giving symbols to the elements the first letter of the name of the element was used. But in case of two or more elements with same initial the next elements were given symbols containing first two letters. Since boron has symbol B, so bromine got the symbol Br.