喽 is a cheerful spoken variant of 了 used to announce or call attention to something. Very informal, avoid in writing. There is also a toned reading lóu, bound to 喽罗 (a gang's underlings or minions), the only common word that uses it.
grammar
喽 is always sentence-final and carries a light, upbeat tone. It softens commands and makes announcements sound friendly.
Left mouth radical, the indexing component. Marks 喽 as something spoken, fitting its role as a sentence-final particle. Same radical in other speech-particles like 吗, 呢, 啦.
Right 娄 supplies the sound; the toneless lou is a colloquial weakening of lóu. This is the simplified form of the right side in traditional 嘍, a pure phonetic shell for the particle reading.
