I wouldn't buy that sign even if I was a billionaire, because I don't see any significance in it. Yeah a dude held it and it generated some hype in Bitcoin community for a week - so what? In my book that wasn't a significant moment in Bitcoin's history. The fact that it was sold for $1M is just another example that there are Bitcoin whales who sit on large amounts of coins and can easily spend $$ millions on some overpriced stuff.
This is you sharing your own opinion on how you feel about it. On the other side, a lot of us wouldn't try to acquire any piece of paper or art that has no use to us, but these collectors, who like collectibles a lot, think differently, especially those rich Wahala's who are looking for means to spend and make some BTC and make things popular.
What I see here is that some people use money to get more money or fame. That paper is hyped and is the perfect piece to get the kind of attention they need. It could easily be sold out again to another wahala with just a little hype on it.