One thing I forgot was that the Berne Convention (https://en.wikipedia.org/wiki/Berne_Convention) didn't apply in the USA until March 1989 - they had the UCC instead (https://en.wikipedia.org/wiki/Universal_Copyright_Convention), which required registration and the use of ®. Aladdin Sane (https://en.wikipedia.org/wiki/Aladdin_Sane) was created in 1973, so any protection might differ significantly between the UK and the USA. (FWIW I didn't see the symbol in the UK TM DB, though again Ziggy Stardust is registered throughout the EU (https://oami.europa.eu/eSearch/#details/trademarks/000974352).)

The bolt has clearly been used by others (http://www.davidbowie.com/news/instances-aladdin-sane-lightning-bolt-increase-15521), probably not under license. I think at this point it's gone beyond acting as a trademark for the entertainment work of a particular person.