This might be a silly question, but I’m finding it surprisingly hard to answer. A friend of mine works at a barn that acquired an elderly Thoroughbred a few years back and was told he’s an Irish import. His lip tattoo is a little hard to make out (they think he’s 20+), but while looking around the internet I’m only finding references to lip tattoos used on North American horses. I presumed lip tattoos were an international thing, but maybe not? Would an Irish horse have a lip tattoo? What Letter/YOB system is used?
Based on this site, it says “horses foaled outside of North America will (also) have an asterisk at the beginning of the tattoo”.
http://www.horse-races.net/library/lip-tattoos.htm
It also includes helpful information about the tattoo letter/number combinations and how to get more information on the horse’s identity. 
Certainly not common practice to use lip tattoos in the UK. All TB foals have to be microchipped here (and DNA blood tested, I think).
I could ask at the barn, or maybe this is the excuse I need to go visit the Irish National Stud. 
Ivy - Thanks for the link! Not sure how I didn’t find that site…then again I was trying to discreetly research at work and the computers are a bit picky when it comes to “gambling” websites. AKA, anything horse racing, lol.
Shanthi - I feel this is a very good reason to visit the Irish National Stud. For research purposes, of course.