The sign accompanying the suit. It reads
The First Space Suit
A Diving Suit for Space
The Sokol SK-1 suit was the first space suit ever used. It was worn by Yuri
Gagarin on his historic first flight to orbit the Earth. SK-1 stood for
"Skafandr Kosmicheskiy #1," meaning "diving suit for space." After his
successful flight, the suit continued to be used for other cosmonauts until
1963. Sokol SK-1 was a full pressure space suit with a life support system and
was used for flights in which the cosmonauts would eject and land
separately from the spacecraft. The suit included an attached helmet with visor, an inflatable
rubber collar for use in a water landing, a mirror attached to
the sleeve to view hard-to-see switches and gauges, a pressure liner with
connectors for life-support and communications hoses, leather-palm gloves,
heavy leather boots, and a leather-covered radio headset. Valentina Tershkova,
the first woman to fly in space, used a variation called the SK-2.
Other than on Astronautix, this sign is the only place where the SK-1 suit is
referred to as a "Sokol SK-1." I'm more familiar with "Sokol" referring to a
later type of Soviet/Russian
intravehicular suit, a type of which is still used today.
I've also read that "Skafandr Kosmicheskiy" means "space suit", and indeed Google
Translate provides that exact translation.