This is a clear glass symbol tube manurfactured by Burroughs. It can display a plus and a minus sing, the letters "R,M,K", the character AC and an Omega symbol. Maybe this tube was used in a measurement device. The exact type was not determinable, because the print was vanished. Only a Burroughs Logo, the word Nixie, "R07R" and a date code could be identified. I also could not find anything about such a tube in the Burroughs Catalog. The working conditions seem to be the same as the B-8442. If you have any info about this tube, i would be happy to hear about!

Update 12/2018: I got contacted via mail by someone who knew about this tube. According to the email, this tube was used in digital multimeters by helwett packard. It is a special made for HP and was used in the meters 3460A & 3460B with the option "03". The HP part number is 1970-0015 and the burroughs part number is B-5993 Meters with the option 01 and 02 used a different tube than this one! I was very happy to get this email!