The likelihood is that the sticker is there due to the glass unit being in a sense infra-red reflective, that means that it selectively/directionally passes and reflects radiation we sense as warmth. In the UK the preference is for the glass to pass there rays into the house and reflect any from within the house back in. If the installation is the reverse, as is the practice in warm countries, then the sun will not warm the house as it normally would in the UK. This type of glass was pioneered by Pilkington as Kappafloat but now a number of manufacturers and brand names are also available. Check whether there is any other indication of the type of glass.
Thanks for replies, the trouble is we ordered French doors with glass, and fitted our selves, when we installed glass we realised there was a sticker on one side. We fitted this to the outside, that said.. This side in, but was it, this side in, from the out side or this side in from the inside. Errrm