Can I use a whiteboard marker to write on my thunderbolt monitor?
Dry erase markers have organic solvents in them which may cause damage to the optical coatings on the display's glass face. Also, depending on the coatings, it may actually be difficult to leave visible lines with a marker. Without details on the display construction, it's hard to know without trying. Given how bloody expensive the things are, I wouldn't risk it, but I won't say it's impossible.