That is a QR code. Typically it would contain a link to a webpage for more product information. Phones have apps to scan these codes.

https://en.m.wikipedia.org/wiki/QR_code

The sticker is so when it is displayed in a retail store (still the first place musicians get to try out a synth) a walk-up individual can find out something about the keyboard. It is purely for first impression... feel free to remove the sticker, you own the keyboard. See a MODX on display in a retail outlet, the sticker is already in place, you can remove it at your leisure.

The QR code, again, for the walk up customer - they can scan it with their smart phone and be taken to a website to get information about the MODX. Many times there is no one to assist customers in stores, the POP (or Point-Of-Purchase) promotional stuff is often put on new products to introduce it to the market. Sometimes these are placed on the first couple thousand units... to ensure that the word gets out about the product.