Why hasn't anyone put zombies on the "caution illegal aliens running on the I-5" signs?

If you haven't been within 5 miles of the Mexico / USA border, then you haven't seen the big yellow sign with the man and woman running... it's the "Hey! People are running across the border illegally and on the damn interstate, so don't hit them!" sign that is on the I-5 here in San Diego's south side (San Ysidro) on the border with TiJuana Mexico.. and if it had a zombie chasing them... that would be effing hilarious!