Gas shut off valve

Use caution if the valve hasn't been used in a while. You may want to loosen the nut on the other end to get it to move easier. This may cause a slight leak but will stop when you retighten the nut

That appears to be a cast brass ground key valve. They are obsolete and not approved in new work. They seize up, leak or both. Often, when you try to shut it off that cast brass wing will shear off rendering the valve stuck in that position. If you have the opportunity to have other gas piping done in the house, I suggest you have a pro cut that garbage out and replace it with a fully ported ball valve listed to ANSI Z21.15 .Ball valves almost never seize up or leak and, being fully ported means you have the full diameter of the pipe, unlike ground key valves.

FYI, the emergency shutoff for any building is at the meter. Learn where this is so you can direct responding personnel if there is need. Most utilities strongly chastise even pros to shut off, and on their meters. That's because we have this invasive species called "lawyers". In the event of a suspected indoor leak the code does not expect the lay public to enter a space flooding with combustible gas and attempt to shut it off. Exit the building taking the pets and kids if you're attached to them, do NOT turn off any switches or anything that could spark, such as light switches. Just get out and away from the building, THEN call 911. Let the cavalry deal with it.

Things you can do are to maintain a reasonably clear access to and in front of the gas meter, roughly 3 ft x 3 ft without being attacked by vegetation, access doors, or other equipment. There must be a 3 foot clearance from the vent on your meter's regulator to any source of ignition, such as air conditioning condensers, electric meters, shutoff switches, lawn irrigation controls, etc. I pointed out the gas and electric meters were about 18" apart on a job speaking to the technician for the local utility. He quipped the electric meter was not a source of igntion. When I asked if it was rated intrisically safe he just walked away.

Regulators have a vent to the atmosphere that must be maintained clear. That means you cannot bury your meter in mulch, leaves, detritus, etc. It should be located above the local typical snow levels. If you're in a heavy sustained snow or blizzard, go make sure that vent is unobstructed and not plugged with ice or snow. Even when there is no snow around or you're in a warm climate, palpate the bug screen on it annually to ensure it is not obstructed with mud dauber wasp nests, spider webs, rust, etc. if the screen is cruddy, brush it with an old toothbrush or your wife's. Note that if you are standing next to any regulator vent and get a Whiff of Jiff, don't freak out. EVERY time the pressure changes in the house, a TINY amount of gas leaks past the rubber diaphragm and out the vent. It is on the order of parts per million. Now, if the odor is sustained, call for a pro or the utility to investigate and ventilate the space if indoors. Just don't shoot bottle rockets at it to see if the leak has reached the Lower Explosive Limit (about 4.4% methane to air by volume).

HTH