Abou rewso Aqeel (NETTING INSPECTOR)

That's a common question, mate. The simple answer is that 'smile' doesn't actually have a full form. It's not an acronym like scuba or laser. It's a proper English word with its own long history.

What you've likely seen are 'backronyms'. These are creative phrases people invent to fit the letters of a word. A very popular one for 'smile' is 'Sweet Memories In Lips Expression'. It's a lovely thought and captures the feeling well. But it was created long after the word already existed. So, there is no official full form, just some really nice, inventive ones.