John Roberts, from the Shropshire Angling Federation, told the BBC the removal of the fish had become a major problem.
He said he caught three Polish men with pike and a mallard in separate incidents last week.
The signs, sponsored by the Angling Trades Association, have the backing of the Pike Anglers Club and many angling and conservation groups.
They use simple pictograms to illustrate fish should not be killed and removed for the table.
Click here for more on the story. Copies of the signs can be downloaded by going here to the main PAC website.
