Similarly to people telling the OP to ask their question on Apple.SE, even if it's on topic here on SU, I think that there's a general problem with comments like the following:

This should be on Server Fault!
Ask on Stack Overflow!
Try apple.stackexchange.com!

These comments do not serve any good purpose for several reasons.

• They leave the OP confused about where to ask. Was he wrong asking here? Doesn't that even come off as rude?

• They do not have an actual effect on the state of the question. It's not automatically being moved.

• They will force the OP (especially in the case of new users) to re-post their question on the other site, therefore cross-posting. If the community decides that the original question is good to stay, we have a cross-site duplicate. Or, even worse, the question is later migrated.

What, specifically, can we do against this?