The Bangko Sentral ng Pilipinas (BSP) advises the public to carefully feel, look, and tilt their banknotes to check the identifiable security features as illustrated below:
One easy way to determine if banknotes are genuine and not altered is by checking the watermark by viewing the banknote against the light from either side. The watermark in the blank space should be the same image as the portrait on the banknote and denominational value.
The BSP encourages the public to report any information on currency counterfeiting to the nearest police station or law enforcement agency, for appropriate action, or contact the Currency Management Sector for assistance at Tel. Nos. 988-4833 and 926-5092.
Source: Bangko Sentral ng Pilipinas (BSP)