Most of the time I presume users who are active on more than this site notice the cross-post. This is how I notice cross-posts between SO and U&L (although I'm not not even remotely as active there as here).

Sometimes, you can spot copy-paste errors in questions, such as

0
down vote
favorite

where the user has simply copied by dragging across the voting arrows and the favourite button when copying their question from another site. It's then trivial to look for the original question across the network.

Most of the time I presume users who are active on more than this site notice the cross-post. This is how I notice cross-posts between SO and U&L (although I'm not even remotely as active there as here).

Sometimes, you can spot copy-paste errors in questions, such as

0
down vote
favorite

where the user has simply copied by dragging across the voting arrows and the favourite button when copying their question from another site. It's then trivial to look for the original question across the network.