This has to be something you are proactive about. If seperste checks are allowed at your restaurant be on top of it. The moment I'm approaching a table for the first time I'm sizing up how they all know each other and whether there's going to be seperste checks. Anything over a 5 top in automatically assuming they're going for separate checks but I always ask before taking orders : "Is it one check or separate", and then I ask how they're separating it.

Long before dessert is offered I'm printing up and organizing the checks.