Fermilab humor

While visiting Fermi National Accelerator Laboratory (Fermilab) several years ago, I was surprised—and amused—as I approached the main accelerator ring to see this “road sign” directing me to the left if a proton and to the right if an antiproton. Equally surprising, I haven't seen an image of this published in the literature, so I would like to share it with your readers. My students certainly appreciated it, although none of us has been able to decipher any deep physics meaning in the accompanying “NO FISHING” sign. Perhaps just more Fermilab humor?