Specifying short marginal note?

[Dorai Sitaram]

What's a good way to put a bit of text in the left margin of the "current" 
line?  

Let's say there is a special sentence in my document, and wherever it is 
rendered I also want the left margin at that spot to contain some annotation 
(like a pointing hand symbol, or light bulb, or something attention-grabby).  
In general, the annotation can be a whole marginal paragraph spanning multiple 
lines, but I'll be satisfied if only a narrow piece of text (i.e., narrower 
than the prevailing left margin) is allowed.

In the source document, the annotation  will be specified in the vicinity of 
the special sentence. Essentially, I want a footnote, but it goes in the left 
margin rather than the footer, and the marginal-note (I believe this is the 
technical term for this) text isn't required to be multi-line, if that makes 
the implementation any easier.


--d