I wouldn't risk it personally. I'm sure you'd be fine as far as range nazi's go but on the off chance you encounter an LEO it might be a hassle. Lots of us carry the rcmp print out about those mags just in case. If there are no markings, you might not be able to prove it's a pistol mag.
You have to decide if the risk is worth the gain, there should be no trouble, but you could get unlucky. If you're using them in an AR on a range I wouldn't be to worried. I probably wouldn't take the risk using unmarked mags in a Tavor out in a field however.