Clear signs are mold on the surface or a foamy, fermented consistency.
Other possible but harmless product changes:
Hissing Sound: Once the bottle seal is opened, there may be a slight hissing sound. This results from the use of nitrogen in all ActiNovo products. However, this is completely harmless regarding health.
Deposition on the surface: Excess glycerol may be deposited on the surface. If necessary, you can remove the excess glycerol. The stabilizing effect of glycerol may also cause clumping. Please shake the bottle very well and continue your intake as usual.