The story of 'los toros' is a curious one indeed!!!
This is what I know.
They must have been put up in the sixties(or even the fifties), because I'm about to turn 31 and I've seen them all my life. They were ads for Osborne a brand of 'jerez' basically, I think. So the used to have Osborne written across the bulls in big red letters if I remember it well.
About 10 years ago or so, I don't know this exactly 'cause time flies! Osborne was about to remove them; but when the public opinion found out about it, everybody asked that they didn't do it!, we are all so accustomed to see them as part of the landscape, and they are something so unique!; so after some controversy, Osborne reached an agreement with the government I guess, and we kept "our bulls" without any comercial brand attached to them.
So yes, after that they became some sort of symbol even more than before, and now there are all kinds of gifts, and decorative items with a "bull motive".
And they are useful too, because in the past, present and future, Spanish children have been/are/will be entertained by spotting the next 'toro' when traveling by car throughout the Spanish roads.
pim
P.S.: these toros play quite a part in the movie "Jamon, jamon", starring a young Penelope Cruz.