SOFA stands for Status of Forces Agreement. A status of forces agreement (SOFA) is an agreement between a host country (e.g. Germany) and a foreign nation (e.g. USA) stationing forces (military, civilian and contractor) in that country.
SOFAs are often included, along with other types of military agreements, as part of a comprehensive security arrangement. A SOFA establishes the rights and privileges of foreign personnel present in a host country in support of the larger security arrangement.
A SOFA stamp will be placed in the passports of personnel PCSing to Germany. The SOFA stamp shows border control and other officials that you are stationed in Germany and covered by the Status of Forces Agreement, which covers issues like entry and exit into the country, tax liabilities, postal services, employment terms, and civil and criminal jurisdiction.
The SOFA has both freedoms and restrictions. Those (military, civilian or family member) who disregard the standards set by the SOFA could face fines, removal from host nation country and more.