Does anyone produce these, so you could stick it on the body tube, in case you made modifications? It would be nice if all kits sold had the CP information supplied. I assume it's known by the companies(Estes, Quest, AT, etc.) who produce the kits.
If you don't find stickers you like, a little trick I do is to put a trim stripe around the rocket at the CP. if your fins or nose cone are a diferent color, mark and mask a thin little stripe that goes around the rocket at the CP location and spray the stripe when you do the fins/nose. You can also do this with monocote trim if you like. You can even do multiple colors. Vary the width or pattern of the stripe as your moods dictate.
The stripe looks cool and you'll know what it is for.
BTW, CG will differ depending upon the motor you use, how much wadding you use, how far down the parachute has slid, etc. so it's not as useful to permanently mark the GG. CP on the other hand will not change unless the design of the model changes.