Glass ramekins - numbers at the bottom - heatproof?

[pikapoo]

Just cleared out a kitchen shelf to discover we have about 30 glass ramekins O_o (the kind supplied with supermarket/GÜ desserts). Some are branded GÜ and some aren't.

Many of them (mainly the unbranded, non-GÜ ones) have various numbers etched on the bottom (see pic for example). This is a random question but does anyone know whether those numbers are indicative of how heat-proof the ramekins are? I need to declutter but don't want to accidentally throw out the heat-proof ones!

No idea about the numbering, but they should be fine - they're usually made of Pyrex type glass so the only thing you can't do with them is put them directly on a heat source. I went through a similar exercise recently and only kept sufficient to make something like 8 dessert servings - I was never going to use 24.