Surplus

The Supply Sergeant on Hollywood Boulevard. Not a really big store, but it does have a big sign. 

There was clearly a point at which such a sign was needed, to draw people to this store rather than another. But another what? 

Another surplus store? They used to be more common, certainly - there were at least two in the East San Fernando Valley that have been gone for years - a third, counting a recent closure on Van Nuys Boulevard. Or was surplus just another clothing store at the time the sign went up? Surplus was a good place for camping gear in the 1970s - although already getting competition from REI and Sports Chalet. In Cars, Sarge's Surplus Hut has literal artillery, which is (probably?) more than these places ever really did. Knives and paintball guns appear to be the extent of actual weaponry at The Supply Sergeant, although there might have been more than that back in the day. It mostly has, well, camping gear and clothing (uniform parts, used and new, along with blue jeans and working clothes) .

Between the size of the sign and the khaki-clad soldier on the sign, this would appear to be about 60-70 years old. A cursory Googling indicates that, as expected, military surplus stores were (no surprise) big after WWII. The U.S. government, in particular, had plenty of excess military supplies that were no longer needed. Buy large lots for pennies apiece, get other general purpose items, charge appropriately => Profit!

And a slightly less cursory Googling gets: Yep, opened soon after the end of the war.