Being that this is quite a widespread Badge and little has been written about it I thought I'd fill in some blanks.
The Badge was proposed on 23rd April 1934 and established by the People's Commissariat Of Lines Of Communication Prikaz of 29th April 1934. Although established by a "ministerial" Prikaz it was terminated by Decree Of The Supreme Soviet Of The USSR on 16th September 1957.
There were c80,000 serial numbered examples and around an additional 400,000 non-numbered examples. The majority, if not all of the serial numbered examples were awarded before the Great Patriotic War with mirror-back examples with an "NKPS" screwplate making up the majority of GPW awarded Badges. All "MPS" (Ministry Of Lines Of Communication) examples were produced and awarded after March 1946. The Badge was awarded during 8 administrations of 6 different "Ministers".
The first Type of this Badge was of a three piece (plated copper/brass) construction but was soon superseded by a single piece (plated copper) construction.
The design of the Badge features three Red Banners, a nut, a red star, a hammer, a sickle, two (later one) ears of wheat and most predominantly an IS20 (Joseph Stalin) Class Locomotive.
The first IS20 (IS 20-1) was completed in 1932 (pictured) with IS 20-2 being completed in 1933. Although there were only two functioning examples of the IS20 when the Badge was established there would be a further 636 IS20 Locomotives built between 1934 and 1941 making it the second most common of all Soviet produced steam locomotives (behind the FD - Feliks Dzerzhinskij). The IS20 was in service until 1970.
The second picture is the 1936 built IS 20-08 which has almost the same classic profile as the Badge.
Here is a mirror back NKPS mirror-back example with counter-plate. A fantastic example of what can be purchased in Yorkshire for under a £ Pound ($1.60 currently).
I've taken quite a fancy to these recently and the MPS Variants can often be picked up for single digits as hundreds of thousands of these were awarded from 1946.