In this paper, an open ring microstrip resonator used as central resonant element for spectral signature based on chipless RFID tag, is proposed. It has been established a coding through the relation between bits and resonant frequencies, these resonances can be inhibited by changing relative position between ring gap position and excitation port. A 3-bit tag is designed and fabricated using a single open ring resonator on an area of 20×20 mm2. Experimental evidences of the prototype behaviour are showing an excellent agreement with the electromagnetic simulated response. Finally, a strategy for the miniaturization of the structure is proposed.