Deutsche Bundesbahn (DB), Font for lettering:

The Deutsche Bundesbahn (DB) became a railway company in West Germany in 1949.

Coaches - Wagons - Locomotives
When the DB was founded, only the lettering in DIN 1451 middle font was used for locomotives, railcars and the wagon fleet.

AKA DIN-Schrift, as defined by the German industry standard committee in 1931 (confirmed in 1936), under the supervision of Ludwig Goller. 

Used most prominently for German traffic signs, postmarks, and, until 1994, for number plates. 
Spans 3 widths: Mittelschrift, the condensed Engschrift (based on the standard lettering model by the Prussian Railways), and the expanded Breitschrift.

Detailed explanation of the DIN 1451 font here.

Deutsche Bundesbahn (DB) AG uses a variant of the above font, DIN 1451-4, which is available to purchase, at a fairly hefty sum.   

The visible change of the lettering began in late 1950 to early 1951.

DIN 1451 middle font

Coaches.
For the blue F-train coaches the font DIN 1451 bold wide font was also in use.

DIN 1451 bold wide font

This lettering could be in colour or in silver-coloured, raised letters or as a sign.
The RHEINGOLD coaches and the blue F train coaches of group 39 were the first to receive the DEUTSCHE BUNDESBAHN lettering.
The later blue express train cars only had the DB under the window front.

F-train coaches

Passenger coaches that did not belong to the comfort class were from 1951, were either marked with the letters DB or Deutsche Bundesbahn in DIN 1451 middle type.

Standard coaches

Freight wagons.
The same also applies to freight wagons which, due to the large number of units and after the discontinuation of the designation Reichsbahn and the zone markings, were only marked with the letters DB in DIN 1451 narrow type.

Freight wagons

Locomotives.
Diesel

Diesel V200

Electric

Electric E10

Steam

Steam Locomotive