EVERYTHING is trademarkable, and does get trademarked after they come into common use. “Let’s roll.” “Nothing but net.” “Stealth.” Everything.
Like patents on common ideas, it’s a matter of whether someone is willing to spend a fortune fighting you when you sue them. The trick is to sue those with little resources, at least until you’ve built up a war chest and a few wins.
Teresa Nielsen Hayden used the vowel-deletion technique in 2002 for internet forum moderation on her blog Making Light. This was termed disemvoweling by Arthur D. Hlavaty later in the same thread.
Nielsen Hayden joined the group blog Boing Boing as community manager in August 2007 , when it re-enabled comments on its posts, and implemented disemvoweling.
Antinous was still using it when I started as a moderator (2011-ish?), but it was phased out soon after that. I think that’s because we started using Disqus, which allowed people to edit their comments. It didn’t work as well if people could just add the vowels back.