I saw a question (here) that was clearly off-topic and could be (and probably has been) answered on tex.stackexchange.com. However, when I tried to flag it, was given the option of saying it was better suited for our meta site, the math Stack Exchange site, or SO. When none of these options are appropriate, there doesn't seem to be a way of either writing in another Stack Exchange site, or marking it as generally off-topic (see screenshot below). What do moderators prefer or expect users do in this situation? Downvote and/or comment without a flag? Or just leave it alone? Something else? Have I missed something?
Indeed, there are pre-defined migration paths (mostly because off-topic questions on this site are often of potential interest on SO or math.SE). I appreciate that users flag such questions, so that moderators can handle the migration quickly. You can also leave a comment to the OP, but in this case don't forget to remind him or her not to cross-post.