to be acquired separately, either at a local store or online. Both the dimensions of the plates and the typeface of letters and numbers are standardized. After purchasing the number plate, the official stamps must be applied, back at the registration office. A fee is payable for the registration, in addition to the expenses for the plates. Changes, such as a vehicle being sold or its owner moving residence, must be registered to keep the vehicle documentation up to date. If the vehicle remains within the district, the licence plates may be retained. A vehicle being relocated outside of the district has to be registered at the authority now competent. Whilst it was mandatory to have the plates altered, according to the current address, this obligation was reduced in 2015 and has meanwhile been abolished. Since then, it is generally not possible any more to tell the owner's district of residence from the area code on the plates, as they may have registered it at a former residence e.g. in Hamburg yet moved to Frankfurt meanwhile. When owners choose to deregister their vehicle, the officer at the local authority will want to see the licence plates with defaced seals on them as proof that the plate can no longer be used in public. For this purpose, special machines are available for use at the registration office. Once defaced, the plates may only be used legally on public roads for one return journey to the owner's residence. If a vehicle is to be deregistered and a new one registered to the same owner, it is possible to swap the licence plate from old to new within the same process. Documentation and fees are necessary nonetheless, and neither vehicle should be used to reach the authority, as the assignment of the number changes by the minute. It is general practice for owners to deregister their vehicles when selling them, typically when a sale is agreed. A sales contract is highly recommended, and various forms are available online for free. A seller may hand over their vehicle with valid licence plates and papers still in their name to the new owner, and the owner will complete the registration transfer to their name. In a scenario without a proper sales contract, the seller may become liable when the buyer commits traffic violations or even criminal acts related to the car or plates. It is