The ad you designed is in another publication

It was a problem well before the digital age: a publication takes time to create an advertisement for a special client, and then that ad starts appearing in the opposition papers.

With the newspaper Worsley Press used to own we would include a box on most proofs stating that the design of ads where we did the layout was our copyright and could not be used elsewhere without permission. I think it included a statement that a reproduction fee would be charged, though I don't think we actually ever tried that. We also wrote to the publishers involved reminding them of copyright law.

Other suggestions: include the name of your publication in the 4pt code on the ad that identifies the file, and maybe include a copyright symbol. No publication likes including another's name even in tiny type.

But nothing will work if you cannot persuade the client that they should not submit ads created by you to other publications unless they are prepared to pay you a design fee. Most businesses which do not employ advertising agents or design bureaus directly simply do not understand that there can be any restrictions on something which is based on their words.

Finally, get your sales people to start pointing out to potential advertisers that your designs are so good, that others can only copy.

I won't suggest that if copying becomes too blatant, that you do what we did once -- include a deliberate error in the proof then correct it immediately so there's no danger of it creeping through. Then wait for the mistake to appear in the opposition. Phone numbers are good for that ;-)