A tetraphenylethylene-derived compound, TPEPhDAT, has been prepared by successive Suzuki-Miyaura coupling and ring-closing reactions. This compound exhibits aggregation-induced emission (AIE) properties in the DMSO/MeOH system, with a fluorescence emission intensity in the aggregated state that is 5-fold higher than that of its counterpart in a dilute solution. Moreover, the diaminotriazine structure of the molecule is a good acceptor of protons, and thus the TPEPhDAT molecule exhibits acid-responsive fluorescence. TPEPhDAT was protonated by trifluoroacetic acid (TFA), leading to a fluorescence quenching, which was reversibly restored by treatment with ammonia (On-Off switch). Time-dependent density functional theory (TDDFT) computational studies have shown that protonation enhances the electron-withdrawing capacity of the triazine nucleus and reduces the bandgap, producing a more intense intramolecular charge transfer (ICT), thus leading to fluorescence quenching. MeOH can easily remove the protonated TPEPhDAT, and this acid-induced discolouration and erasable property can be applied in anti-counterfeiting.