[dekeguy]

At my US school, team letters were awarded under specific criteria and jealously garded against unauthorized use. Sweaters (with sleeve rings for multiple awards in the same sport) were for lettermen. Jackets were reserved for state championship team members and were provided by the school). No one would dare wear a school letter that had not been earned and awarded by the rector. Academic letters were so hard to earn that they were highly respected as well. Sweaters only, no jackets for academics. Sports letters were block capitols. Academic letters were Old English Script.

At my UK school one could win colours which could take the form of a cap or a tie in sporting colours. During normal school days one wore the usual school uniform but could wear coloured rings woven into the top of one's socks to show your team/organization affiliation.

I agree with the comments that wear of a school jacket with a team letter might not go down too well. Your school's letter is something you should earn. It really should not be a fashion statement but a reward of recognition for participation, skill, and effort.