I'm not a cop. I've known a decent number of criminals. One pimp that I used to know, casually, carried a Sig 230 or 232 in an unknown make leather holster. He was upscale in his dealings and probably even had a carry permit.
A common and useful expedient, advocated by Workman Guy from his semi successful stint doing strong arm robberies - was to cut the top off a bubble envelope and fit in your pocket. This actually makes a decent improvised holster.
During my crackhouse dwelling phase, one of the local dealers that threatened me via a hand on his the butt of his auto (looked like a Hi Point) looked as though he had it crammed in a clip on nylon holster. This may have been because one local dealer could usually be talked into giving such as a "throw in" with a sale.
We also found an old leather holster, possibly homemade, along with a box of .38 SW ammo with five rounds missing (and a box of 16 gauge slugs with one round missing) abandoned in an apartment, the two former occupants of which had apparently robbed the denizens of a different apartment (reportedly armed with a sawed off shotgun and a top break revolver). Whether they had the holster with them during the robbery I don't know, they certainly didn't find it worth taking along.