This is a very rare type indicator tube. It was only used by Zenith Corporation for their high end radios and ONLY in the model year 1938. They went to a more common 6U5 after that year so if you have a Zenith radio from that year (such as a "Walton") then this is the correct indicator to use in it. The photos are taken in ambient light with a tester that has no shielding so it will show up better in your radio...
The first picture shows zero volts on the grid which would indicate no station is tuned in. The second photo shows -18 volts on the grid that would indicate a strong station tuned in.
The outer ring is gone and there is green in the field. There are some spots missing but it will still help you tune the radio. The item "ZENITH 6T5 target eye tube about 50% or so good (see pics)" is in sale since Tuesday, December 7, 2021. This item is in the category "Collectibles\Radio, Phonograph, TV, Phone\Radios\Tube Radios\1930-49". The seller is "chinobob" and is located in Tacoma, Washington. This item can be shipped worldwide.