DD is 19mo. She can recognise and say A, P, M, B, O, S, E, U and L. Am I being totally PFB to think that's pretty cool? 
Her speech is really quite behind her friends', and she only has about 30 or so words that are recognisable. (Although she is bilingual, so that might have something to do with that.)
My mum taught her M, P and A last weekend, and I've been telling her the names of letters she points to ever since, and those are the ones she can remember. She can say them if I draw them for her, and she also picks them out of her letter magnets and presents them to me proudly 