First of all, are you SURE it says "90" and not "06"? I find it hard to believe that a pigeon that is 19 years old is still racing.hi
a blue bar racing pigeon fly in with my pigeons it has three rings one race ring with the year etc and one red rubber band and one yellow with one number on it what do they last two mean i know about the racing ring i was thinking maybe i could keep this bird the racing ring says
GB 90 C 84958
Second, you really should try to find out who the owner is and contact them. They may let you keep the bird, they may want it back, but it's not yours to keep without trying to get it back home where it belongs.
The red rubber band is a countermark I imagine, which means the bird was in a race possibly and has gotten lost/off track for some reason.
The yellow band with the number 1 on it is most likely a way of the owner identifying what bird it is.
Just in case, here is where you need to report the bird: