I've find pictures very useful, a few screen shots of different brands.
Looks to me like there are many XO sauces out there so they might recognise the pic?
The term 'XO' can be slightly confusing as it's been purloined from things such as 'XO brandy/cognac' (originally meaning 'eXtra Old') to mean something of matured high quality and you'll sometimes see the prefix slapped onto other products which are not Hong Kong-style XO sauce to give them this marketing distinction.
Look out for place of manufacture (HK) and ingredients (dried scallop, shrimp).
Lee Kum Kee brand is a safe bet and I've been coming back to it over the years having tried quite a few others.