On the ride to work today, I discovered that I must have gone past the minimum insertion marker. Not a pleasant experience, but fortunately, nothing is broken aside from my hind quarters. I'm going to track down a set of wrenches to get the seat back in place and tighten it down.
But the seat post has no markings as to what would be the proper minimum insertion (that, or the rust that has built up has obscured the minimum insertion point, its a 28ish year old bike so that wouldn't surprise me). So I wonder, what would be a safe bet? I'd just fudge it and guess but I don't want to go through this again on the way home (though, I have tools there so it wouldn't be as bad).