Why promote yourself at the expense of others? Just say something positive about yourself.
I agree 100% with madstack.
I have a friction tunnel and could put a sign up that says no-scratch automatic, and so could a bunch of operators on this site that have friction IBA’s because we don’t scratch cars either! I would not have loyal Mercedes, BMW, and Porsche (yes, I have many of each) washing with me if was damaging paint. In fact, people who own cheaper cars would not stand for that either!
The picture you posted does not look like car wash induced brush marks to me. It would extend further down the side of the car. Properly operated and maintained friction washes do not do this and it would be best not to lump all operators of friction machines into the category of damaging paint if they are not guilty of doing so.
I am surrounded by some poorly maintained and poorly run touch free automatics that deliver terrible results. I never, with a sign or verbally, criticize any touchless competitor because they are not all poorly run and I don’t want to categorize the good touch free operators with the bad. The customers can and will figure that out.
Again, point out what you do well and avoid signage/comments/attitudes that criticize your competition. Let your work speak for itself - that is what your quality/successful competitors are already doing anyway!