There are two types of bird leg bands, open bands and closed bands.

All parrots that were legally imported into this country and went through quarantine have an open band that indicates the port of entry and an identifying number. These bands are not overly useful for ID as they can be pried off and put on to another bird. There have also been a few incidents of birds getting caught on wire, etc. with an open band. According to my vets, if the band is properly applied, the correct size, and doesn't bother the bird, they generally leave it on. You can buy open bands, but the only use I can think of for them is to identify breeders that are kept in a community flight.

Closed bands are applied by the breeder when the bird is a baby (exact age depends on species) and are designed so that the band is too small to come off over the bird's foot once it is fully grown. A closed band can not be put on an adult bird, only a young baby whose feet are still smaller than adult size. Therefore, an intact closed band proves that the bird wearing it is a domestically-bred baby and provides identification. Organizations such as the Society of Parrot Breeders and Exhibitors, the American Federation of Aviculture, the American and National Cockatiel Societies, etc., sell closed bands for their members that =generally= provide the following info:

Issuing organization initials/logo, Breeder's unique ID code, year of hatch, state, and a number that identifies that particular bird. A breeder who keeps good records can provide you the exact hatchdate, the parents, whatever genetic info they have, and other misc. info about that bird if given the band number. Most of these organizations keep contact records for the breeders, so if you call the AFA with a band number, they can put you in contact with the breeder. For example, my ACS band code is 57E, so the 23rd tiel I banded in 1996 would have the following on its band: ACS 57E 23 96. (The year is usually sideways on the band.)

Several commercial companies also sell closed bands that can have on them an ID code, the state, the year of hatch, and the bird's number, or less or more than that. L&M keeps some records and may be able to put you in touch with a breeder who uses their bands, but a non-organizational band doesn't tell you what company it was purchased from.

Now, to make a long story short, if your bird doesn't already have a closed band, you can't put one on, and there's not much use in applying an open band. Consider another form of ID, such as DNA gene typing, microchipping, tattooing, etc. If your bird DOES have a closed band, it's a permanent ID card and both you and your vet should have a record of the number in case the bird is ever lost, stolen, or needs to have its identity verified.