Air bag light don't come on

Front air bags will not deploy accidentally from mishandling or system problems unless you really work at it to cause it. In your case it is not going to protect you in a crash either because the system is likely dead due to tampering. It is always possible the bulb is simply burned out, but they only turn on for six seconds each time you turn on the ignition switch. That is hardly excessive, and it's real rare to actually find a bulb burned out.

What's more common is someone removed the bulb to hide the fact it was indicating a problem existed, or they removed two fuses for the system. There are always two fuses for air bags and anti-lock brakes so if one blows, there's a second circuit to run the warning light. Either way, when the warning light stays on, the system has been turned off automatically and won't do its job when needed, and when the light never turns on, you can't be sure if it's just the bulb or if the system has been disabled.

Your mechanic can connect a scanner and see if it can communicate with the Air Bag Computer. If it can, he will read the diagnostic fault codes if there are any. If the scanner won't communicate, the system has been disabled, or less likely, the computer is defective.