This paper illustrates the posture effect on Ultra High Frequency (UHF) RFID tag detection. The originality is about the polarization characteristic of passive tag and reader antennas. Different orientation of the passive tag could make the polarization loss distinct, resulting in the variation of the Received Signal Strength Indication (RSSI), for instance, placed in horizontal and vertical orientation, will make RSSI distinct. With the variations of RSSI, a control mechanism of 'On' and 'Off' signals for Vision Impaired Person can be achieved. A prototype RFID system and test cane with tags are designed and tested to prove the feasibility.