A Chemical Spill or Toxic Liquid token. The spilt dangerous liquid is spreading across the token and bubbling up as it dangerously reacts with objects it comes into contact with.
The token sits on a 1 inch (2.54cm) base and is approximately 0.236in (6 mm) high. It was originally designed for Extreme Danger, an expansion to the popular cooperative board game Flash Point: Fire Rescue.
A set of 5 Chemical Spill Tokens can be viewed
at this listing