That's just dust spam. Anyone can send any OP_RETURN to any address. It doesn't mean or prove anything.
If someone wanted to broadcast a message to prove ownership of the address on-chain, he'd do it from that address.
Sure, but address gets dusted with OP_RETURN saying "Our client has taken constructive possession of it" on 2025-07-02 and then two days later on 2025-07-04 it gets emptied, after staying dormant for 14 years since 2011. I think the timing couldn't be more suspicious, and if i had any claim to if I'd at least reach out to Salomon Brothers to confirm validity of the message. Not sure why someone or reporters hadn't validated it with them yet.