According to my dictionary (小学館日中辞典) under the entry 天秤 (tenbin) is the gloss 天平 (tian1ping2). It then goes on to give the example:
天秤で量る (tenbin de hakaru)
用天平称 (yong4 tian1ping2 cheng1)
"Measure with a scale."
That is to say, the Japanese word 天秤 is written 天平 in at least simplified Chinese. So, I would say your tatoo means "scale" in Chinese (simplified), and the Tempyou Era in Japanese.
"Libra," on the other hand, is written the same way in Chinese as Japanese -- 天秤座 -- and read Tian1cheng4zuo4.