I think so too. Yes, I have heard of that. People who speak English usually say lol (laugh out loud) or lml (laugh mad loud) and there are many others that are similar. People who speak Spanish will use jajajaja because in Spanish the letter j sounds like the letter h. I think its okay if you say 555 because I have already recognized what it means. By the way if you ever don't understand what I am saying or just have any questions for me I will be happy to help you understand.