Home and Distant Signals

Among other reasons, due to the different developments in both parts of Germany during the Division, German Railways are currently using seven (!) different signal systems.

The signal systems that are currently in use are:

The traditional semaphore signals (Formsignale, literally 'shape signals') where the appearance ('shape') of the signal determines its meaning.
Note that semaphores are not really a signalling system of its own, but belong to the Hp system described below.
The semaphore signals are equipped with lights for night visibility. They are used (with only negligible differences) both with DB and DR. Note that the semaphore signals are almost extinct, but on some spots you will still see them.

The systems of colour light signals (Lichtsignale):

The Hp system that was introduced in 1935, but was (and is) mainly used by the DB, is based on the aspects that are displayed by the semaphore signals at night.
The Hl system that was introduced by DR and is used in East Germany, combines main and distant indications in one signal head. The Hl system is also unofficially called the ОСЖД (OSShD) system after the East European Organisation for the Cooperation of Railways which standardised signalling systems in the former COMECON states.
The Ks system which was designed after the Reunification and is to ultimately replace both older systems. This system also combines main and distant indications within a single head. Ks means Kombinationssignal (combined signal).
The Sk system, which was introduced as a test installation on a single line only, where it is still used today.
The LZB cab signalling system

At the electric urban railways (S-Bahn) in Berlin and Hamburg, special signals are used. These system was invented in 1928, and was the first German colour light system. The S-Bahnen are isolated systems, but are operated by the DBAG, so their signalling goes in here as well:

The Sv system which is used in the urban railways in Berlin and Hamburg.