What kind of pen/brush do 水笔 and 签名笔 refer to?
圆珠笔 simply refers to ball pens. No questions there regardless of the dialect or personal usage preference. 

签名笔 could be referring to gel ink pen in common sense. But for artists I highly doubt that. A good possibility is technical pens. I am an architect myself and this is essential for anyone who wants a clean drawing. 
https://en.m.wikipedia.org/wiki/Technical_pen

水笔 is definitely not water color. It's a formal term for pen.