I did an outside sign that has been painted with acylic paints. Should I seal this with clear laquer to prevent the paint from running?

I see that Rust-Oleum has bought Modern Masters. Does the Master Clear supreme clear coat cause white paint to yellow?

That sounds like a great idea. Rust-Oleum Stops Rust Crystal Clear Enamel will seal the surface and is non-yellowing. We suggest waiting about 5-7 days before applying the product over the acrylic to make sure you have your desired results. - Rust-Oleum Product Support 1