Police in Texas arrested a man for warning other drivers about a speed trap.

Ron Martin made a sign that said “police ahead” and got on a busy Frisco highway, where he waved the sign around. Police say drivers then began to slow down and wave at them.

Martin said he feels speed traps are unsafe.

Authorities arrested Martin, who they say has done this before. He was arrested for having a sign on public property, since warning people of speed traps is not illegal.