Do not know US law.
In Europe just search trademark base and check what is protected. It takes some time and you must study Viena Classes first but online database is free:
oami.europa.eu/CTMOnline/RequestManager/en_SearchAdvanced_NoReg
Professional DB searching by pattent attorney is not free (100 - 600 Euro per TM depending of date)

BTW I'm sure that all US characters are registered in both US and EU bases.