Okay, it seems that the readily identifiable spambots are a rather recent invention, as these are the earliest I could find in my (admittedly cursory) search.
http://www.subsim.com/radioroom/member.php?u=260753
http://www.subsim.com/radioroom/member.php?u=260762 (Note that this one has a post, but it seems highly likely that he is, in fact, a spambot)
http://www.subsim.com/radioroom/member.php?u=260772
There are many old accounts that seem to be spambots, but they have nothing to identify them as such.