Mostly it's been said, but I'd like to add one point about the difference between sig lines and emoticons. Emoticons add a dimension of meaning to a post that is missing from the normal communication; meaning that is generally communicated by body language of one sort or another in face to face spoken language, so they have redeeming social value. They can get irritating if they turn into motion gifs, but even then, they are generally small and not so bad. An equivalent of signature lines is the little pictures associated with individual posters that are sometimes seen on message boards, but they don't carry the sometimes apparent didactic baggage that verbal signature lines do and they perform the useful function of giving a quick ID of the poster. They can get severely irritating if they get big and are motion gifs. I have seen a board where they got so out of hand that there was a minor war created. Fortunately, the people on that board were sufficiently community to keep it from turning into a destructive flame war.

Aside to mg: Your sig line about serving the board reminds me of that line that seemed to show up in every '50s generation ship sci-fi story, "The ship is all! Praised be the ship!"