51 14... Instructions for attaching number/letter designation combination: Removing
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2014 BMW X6, 2013 BMW X6, 2012 BMW X6, 2011 BMW X6, and 2010 BMW X6. However, it is still accessible from the selected car via links, so may be relevant.
Coat nylon string or strong yarn with tensides (e.g. washing-up liquid).
Cut through adhesive layer and remove model designation (1) from rear lid (2).
Remove remainder of adhesive layer with adhesive remover (sourcing reference: BMW Parts Service).