I go shooting with several friends and sometimes it gets hard to remember which mag belongs to who. I’m looking for an easy way to mark glock, ar, ak, and ruger mags. I was thinking colored electrical tape, but wasn’t sure if this would wear off and leave a residue. Not damaging or changing the mags is a major issue.
Any ideas?

i use little colored stickers that my girlfriend getss at work.  1\4 inch sticky dot that i put on the plate. i even go as technical as different colors for differnt types of ammo\caliber. its easy to tell what kind of round, but im an organized freak.

Any mag that protrudes is easy to identify, the AR/AK and possibly Ruger (which Ruger) is simple.  The tape idea, like colored duct, etc.
If it leaves a residue that comes off w/ a little WD40 or "goof off".  On the duct tape I'll sometimes use a sharpie, when I'm testing mag/ammo/follower/spring combinations.  If there's amag that's consistently or repeatedly a reliability issue, I'll mark that too.
Magpuls work but are more expensive than tape.
An orange vs. green or black folower will work but only when empty and not always at immediate glnce.
The glock mags will be a little more difficult.
You can "slightly" mod. yours w/ a dremel'd dimple under the base plate and w/ a crayon or wax pencil fill the dimple, wipe the baseplate the wax will remain and stay in the dimpled recess, re-do as necessary.
Or for the Glock, grab some replacement baseplates from Pearce Grip co. and replace yours, its a non-perm. mod. that allows you to reverse the mod.  They have the same dimples already integrated for this exact reason.

Hope it helps lots o' luck.

/S2

I belong to a fire department and county technical reacue team.  For general marking of equipment All of my private equipment is marked with paint markers.   You can get these at the arts and crafts stores. The habit of marking my rescue gear has followed thru at just about all my stuff that may get mixed with other persons belongings (work tools, ar mags etc.)     Remember if you die we split your gear

You could use engraving to put dots on the baseplates. Use a combination that will be recognized by only you. It will not detract in this case if you decide to sell. At work we use a electric pencil to put the organization on it.

I just use a sharpie permanent pen.  It's not the fastest way to recognize your mag as you have to look closely for the marking but it still shows up plenty good when all you really want to do is identify YOUR mag from someone elses at the end of the day.

If you decide to sell it, and if it isn't a soft moly coat like the early Colt/universal 20's, Gun Scrubber or brake cleaner strips it off with very little rubbing. (I stick to marking my Adventurline 20s or mil-spec 30s)

Sly

I use UNI paint pens.  Removes easy with brake cleaner.  I number them all, too.

I usually wrap my mags with several layers of 90mph tape/paracord at the bottom.
Most people don't, so i know their mine.

If the mag contains a special load I use a sharpie to write the bullet type/grain unconspicuously on the tape-So I don't end up bumpfiring 2 30 rd. mags of BH 69gr. SMK!ARRGH![banghead]

I will also suggest the paint marker

I number my duty mags with whiteout. Works well, and lasts about 6 months.