Cattle grids or speed bumps
For hazards running across the road like rail tracks, cattle grids and speed bumps, outstretch your arm, point to the floor, and draw a line horizontally back-and-forth aligned with the orientation of the hazard.
If a hazard of this type is even close to being in line with the direction you’re riding, such as tram lines or the long, thin grooves which appear at the joins of asphalt, trace that line clearly in the direction it runs to point it out to your fellow cyclists.
This signal can be used to indicate any hazard which runs across the road (and therefore can’t be avoided). These include cattle grids, speed bumps, level crossings, ramps etc.