You would need to be more specific. You could be referring to the serial number, the caliber, a model number, armory/arsenal markings (in the case of surplus military arms), etc.
Blue Book of Gun Values
Yes, depending on who made it and if records survived.
Impossible to answer without knowing what you mean by illegal handguns.
Not normal. Frowned upond by the Federal Gov't and can result in big fines and jail time.
Because they're afraid President Obama will outlaw the purchase of handguns in the near future.
Yes, handguns have a serial number.
You will have to specifiy if you mean commercial production for public sale or custom production.
Yes, handguns were used in WWI, and WWII.
Most historians believe handguns were first invented in the mid 1400s.
In most U.S. States, handguns don't require registration.
rifles are for further range compared to shotguns, and handguns are not as powerful.
There is a safety catch on most handguns that will prevent premature firing. There are gun locks that can be purchased or lock boxes to ensure safety from firing. Actually, that depends on what you mean by "safety catch." Most modern handguns do not have an external manual safety, but all modern handguns have internal safeties that keep the gun from firing unless you activate the trigger.