The IN-4 is a medium sized Nixie tube from the former Soviet Union. The bullseye marking indicates that this was made in the Gazotron factory in the Ukraine.
This is quite an interesting tube as it can be driven as either a regular Nixie tube or a biquinary Nixie tube depending on how the pins are connected. Most drive it as a regular Nixie tube.
Datasheets:IN-4 Nixie Tube