Signing prints, what ink?

If you're using ink I would suggest that you use acid free, archival inks. One such option (and what I use on papers which do not accept pencil sigs) is Sakura Pigma Micron pens. They come in many tip sizes and several colors (including black and blue). They are typically available at independent stationers, art supply stores, or on line at sites like dickblick.com.

My local stationer carries many sizes and colors, but some on-line sites have just black, or prepackaged sets, etc.

Here's a link to some at Dick Blick's: http://www.dickblick.com/zz207/02/ (scroll down)

Sakura offers some roller ball pens with archival inks as well (Gellyroll) but I've not tried them. http://www.sakuraofamerica.com/

All the fine art prints I have seen have been signed using pencil, I am not sure why. I think since it is just pure carbon, it is archival and non-reactive. If you have that option, it is probably good. Otherwise I would just use a traditional pigment ink, such as the ones they sell for fountain pens.

Faber Castell makes a felt tip pen called "PITT artist pen" in black and brown (other colors too) and also 3 or 4 thicknesses like fine, medium, etc. They almost look like pencil when applied but don't smear. Best I have used so far.

http://www.faber-castell.us/docs/index_ebene3_asp_id~17325_domid~1010_sp~E_addlastid~0_m1~14785_m2~14794_m3~14804_m4~17325_suma~.htm

Thanks for all the tips, no pun intended!

Neil