We present the development and performance evaluation of a wearable passive UHF RFID tag based on a split ring antenna that is electromagnetically optimized for operation in the close proximity of the human body. The antenna is composed of a single conductor layer and created on a light-weight textile substrate. Our results show that the split ring antenna provides stable performance for the tag placed at different distances from the body, as well as in air. This is an advantageous feature for cloth-integrated tags with generally unspecified antenna-body separation.