Is one allowed to remove (by tearing) a cleaners' tag from his/her shirt on Shabbos?
I have a Book called The 39 Melachos, it says you should not remove as it is a form of ripping (pg.1407)
I'll try to find sources but off the cuff it would seem to be permitted provided one does not tear through letters. Removing manufacturers tags may be a bigger problem.
In the Shabbos Home it brings Reb Moshe Feinstein allowed going out with tags attached by Staples on Shabbos as it is Mevutal(SECONDARY?) to the clothing if one forgot to remove it before Shabbos. Based on Conjecture I am guessing removal would not be allowed according to him. although Reb Simcha Bunim Cohem In the Shabbos Home Volume 2 allows removing the Price Tags.