How do I safely mark up my Sky Atlas 2000?

OK. I didn't take the telescope out tonight (I have my yearly Umpire
Refresher classes until late on Wednesdays at the moment) but I did go
out with the binoculars. I'll have to admit that the Telescope,
combined with a good (better than my trusty Field Guide to the Stars)
Star Map has made me much braver. I used to just look up, identify
the constellations and some of the brighter stars, and then go
exploring, making a mental note of fun things I'd found. No more, I
have a purpose in my observing now. OK, a little war story before my
question.

I went out to find M47, and possibly M46 in the 10x50 binoculars. No
problem you say? Well, although the seeing was OK and the
transparency was good, the limiting visual magnitude here was about as
good as it ever gets, and that was about 3.5, maybe 4. Finding
streetlights can sometimes be a challenge!

In any case, I found a nice star hop from Sirius and easily found M47.
While studying it, there was something to the left that went away
every time I looked directly at it. I marked it's location compared
to the surrounding stars and found that I was actually seeing M46 as
well. To compare relative brightness, I tried to find M67 (I had
never found it before in the city limits) and finally succeeded. The
two appeard to be of similar brightness (although M46 is actually
brighter). In any case, I looked at the star map, noticed a very
large M48, and decided to try for it as well. I found some nice
marker stars (to give you an idea, alpha Hydra was BARELY visible
without binoculars) and quickly located M48. I think I like this one
alot and am looking forward to trying it in the telescope. No real
resolution like there was in M47, but sometimes there was a hint of
tiny sparkles, like very fine gem dust in a mostly dark room.

But, back to my point. At first I had thought that I wanted to draw
the constellations into my Star Atlas 2000 (I have the deluxe
laminated version (black on white)).. I now think that I'm going to
hold off on that for a bit, but I am wondering what would be a good
marker to temporarily write on the maps with (something that will
wash/rub off). Things like comets that I might want to mark on the
map for a few nights but then get rid of.

I know I could just experiment, and I probably will with any ideas you
give me, but I thought I'd ask if you have any suggestions/experience.

Mark