There are some interesting suggestions related to this, including mock-up screenshots, in this other Suggestion: <a href="https://app.roll20.net/forum/post/1241923/allow-mo" rel="nofollow">https://app.roll20.net/forum/post/1241923/allow-mo</a>... The ideas there include Allocating a particular color per-player, and having a pop-up label that tells which player drew any line.