Is it illegal to advertise stock tickers on billboards/social platforms/etc?

I’m having trouble finding an answer to this and given all the turmoil in the markets recently, I’m having a hard time understanding what constitutes manipulation.

Question: Is it illegal to purchase a billboard and advertise a specific stock ticker?

Example: Someone from r/wallstreetbets claims to have purchased a giant digital billboard in Times Square that says, "$GME GOES BRRR", and shows a parabolic chart indicating the stock is "going to the moon".

Is that type of advertising illegal? I’m on the fence, but I cannot find anything that explicitly states it is.

Another example: a group of investors paid for the Tiger King lady, Carole Baskin, to do a shout out on Cameo. They asked her to shout out a stock ticker, which happened to be a veterinarian ticker, and it saw a price surge the group was able to capitalize on. That seems pretty sketch, in my opinion.

Thanks!