The number inside can change, it will usually be 12 or 24 - this refers to how many months you can use the product for, before throwing it away. We use this symbol too, you will find it on our ingredients labels.
We can't speak for high street brands, as they may use some preserving agents - but we don't. Thus, our products have less ingredients, and so may not last as long as the high street version.
Lets take our lovely lipbalms.
These bad boys have a 'use by' of 12 months. This is shown on the ingredients label. We also use the month/year of production as part of the batch number. This is handwritten on the ingredients label, and might say something like RS0415. This means it's Raspberry Sambuca, and it was made in April of 2015. You then have 12 months during which the product is at it's best. You can happily use it afterwards, just some elements may deteriorate slightly. It might not smell/taste as strongly, the colour might have changed a bit. Nothing major.
This is one of the reasons we keep our batch numbers small - so you guys always get the freshest product possible. We would never sell you something close to the end of its 12 months of fabulousness. So don't worry.
As for our other products (like our immense perfume) you can use general guidelines on how long to keep your product. Things like perfume and nail varnish naturally have more chemicals in them than lipbalm (no matter how hard we try!) and so these act to keep the product at its best for longer.
Your best resource for advice on how long to keep beauty products can be found here - this advice applies to our products and any you buy on the high street. The only one I would argue with is Nail Varnish, in my (vast) experience they last an awful lot longer than 12 months.
Hope that's made our labelling a little clearer for you, if you have any questions please leave me a comment of email them to firstname.lastname@example.org