Whoever picks up a banknote or thing lost by someone in Germany may be accused of theft.
🔹According to the law, the person who lost his thing (Verlierer) is still the owner of it (Eigentümer), and the one who found it (Finder) becomes only its temporary owner.
🔹For violation this requirement can receive a fine or a criminal penalty with restraint of liberty.
🔹Exceptions. These rules apply only to banknotes. over 10 euros and things more expensive than 10 euros. If the thing is cheaper than this amount, then you can keep it if you wish.
🔹Where to carry? Or the lost property or the police station. If the find is found on a train, bus or at a bus stop, then to the transport company. 
🔹Lost and found (Fundbüro). If the owner of the loss does not appear within six months, the money or thing is returned to the finder.
🔹Reward (Finderlohn). As a rule, from 3-5% of the total value of the find. Employees of institutions and public transport cannot claim remuneration if the thing is found by them at the place of service.
🔹Keys. When the lost apartment, car and other keys are handed over to the lost property office, neither a receipt nor a reward is issued. It is only necessary to report the place and time of the finding.
There is also a society Schlüssel-Fundbüro Deutschland (SFD), and a metal token will be sent by mail to the person who has entered into a contract with him to attach it to a bunch of keys.
🔹Phone. German police recommend, to make it easier to find the gadget, write down your 15-digit individual IMEI (International Mobile Equipment Identity) number. The IMEI number can be found in the iOS and Android settings or by dialing a combination on the phone * # # 06 
🔹Bicycles. If an insured bike is stolen, a certificate is often required that there is no bike in the lost property office (Negativbescheinigung). You can apply for such a certificate a month after the loss, by presenting an identity card, a sales receipt, a registration certificate, an operating manual, a confirmation of an application to the police, a letter to an insurance company. A fee is charged for issuing a certificate.
🔹Animals. Found pets are returned to the reception (Tiersammelstelle). They are kept there for several days, after which they are sent to an animal shelter (Tierheim).