If a forum doesn't allow me to show up as hidden, I simply abandon it. While an administrator may find it creepy one wishes to hide, I find it equally disturbing an administrator is fixated on seeing me online. Forums which I stay hidden on are meant so because I like to read old material or do a few searches. I don't wish to be bothered by PMs if someone sees me online and wishes to send me a PM. One could argue I'm under no obligation to respond to a PM right away, but humans simply don't understand the concept of others not having time. It would offend the average person if I held back from replying to them for up to 10 days if the matter wasn't remotely urgent. I can't do that if I'm made public, but I certainly can if hidden. It's also why I choose email over other mediums of communication.