In 2008 my programming skill was too weak, so I ordered nixie (neon glow tubes) clock kit. I had lots of ИН-12Б tubes in my stock, so I used them as my starting design. Tubes were connected to clock PCB with tube sockets, so I had option to swap and test some other tubes.
In this series of tubes there several special tubes like ИН-15 and other. They have various symbols instead of digits.
This clock set is based on PIC16F876 MCU, there is step-up power suply on board.
For more information check original web page in Lituanian language (comments have some interesting links).