i have another YSL with an identical logo. although i dont use it on a daily basis, when i do use it, i avoid touching the logo at all costs. because it is stamped/painted on, and not an actual 3D logo, i do fear that sweat and other substances may cause it to lose colour. try contacting YSL. not sure whether it'd be covered...
we had a similar problem with Ferregamo, where the metallic colour (entire wallet) came off a LOT. ferregamo blamed us for having sweaty hands...i mean how do you want me to hold the wallet? with gloves?