Serial number. Go to Browning's site, click on support, then date your firearm.
The barrel will have 'Made in Belgium' on it. The receiver can be dated by serial number.
It will be marked "Made in Belgium"
The barrel will be marked "Made in Belgium"
Comparison to known grades.
By the serial number.
There were at least three places where the Browning shotguns were made: Belgium, the US, and Japan. Take the gun to a gunsmith and he may be able to tell you easily.
Call Browning, give them the serial number, and they will tell you the age and a host of other information about your gun.
look under the forearm
No way to tell with the information you have provided. Need description of all markings.
Belgian proofmarks, year of manufacture, barrel inscription. == ==
500 USD give or take
You can contact Browning Customer Service through their website, or look up date of manufacture on same website.