They are all over Spain.
I understand they are an old advertising hoardings. Now banned because of their size but the authorities allowed the bulls to stay.
I like a Mahou but prefer a Cruzcampo - although now owned by Heineken. I'd thought a sample a few of the dark versions (just got back from the Seville area) but could only get a Mahou. Horrible - tasted like Murphy's with a Special Brew top.
Not Spanish and probably not very popular in Spain who have much better beers.
I'd happily buy a pint of Cruzcampo.
San Miguel (I think) isn't very Spanish at all historically, well it comes from The Philippines which was under Spanish control at the times. You see it in Supermarkets but...