This is a specifically Cajun French expression meaning “Let the good times roll!” which is often said around the time of Mardi Gras celebrations in New Orleans. There are a variety of spellings used to write this phrase, some of which are listed below. Despite being used in public events and promotional materials, all spellings are incorrect except for the first one:

Laissez les bons temps rouler (correct)

Laissez le bon temps rouler 

Laisser le bon temps rouler

Laisser les bons temps rouler 

Laissez les bons temps roulez

Laissez le bon temps roulez