Some of the hints are in the names.
If they call wheat egg noodles 'mee' or 'mi'
If they are a Chinese restaurant named 'Kim Tar' (this is the old Teochew name for 'Phnom Penh')
If there is an old uncle pottering around tasting and being difficult about food quality
If they have a fried shrimp roll dish that sounds like some permutation of 'hae jor'
If any dish with beef sounds like 'goo' (the Teochew word for beef)
If they offer a noodle soup with the soup on the side (dry style)
It's probably Teochew
I've eaten the same dish in Pontianak, Bangkok, Paris, Singapore and San Francisco, just with different names!