Time Warp Plates (タイムワーププレート,Taimu Wāpu Purēto?), also called Past and Future Signposts, are types of signposts on Little Planet that appear in the Sonic the Hedgehog series. They allow the player to travel between different time periods, namely the past, present and future of different Zones.
Time Warp Plates are slightly smaller versions of signposts, that are colored yellow, grey and black. The sign reads either "Past" or "Future" with yellow font. The symbol of signpost can be seen at the left hand corner next to Lives hud after moving past through time warp plate.
Sonic the Hedgehog CD
In Sonic the Hedgehog CD, running past the Time Warp Plate in gameplay makes the signpost flip once while a voice states the particular signpost's name at the same time. Afterwards, the player must build enough momentum to break the sound barrier, and warp in time while the signpost's HUD symbol starts flashing. When the player gains enough speed, the screen flashes and transports the player to another time. If the player fails to build enough speed, the symbol disappears and the player must try again at another Time Warp Plate. It will also disappear if the player runs past the Goal Signpost before the Bonus Plate. When the player is transported to the past or future, the player's life icon is replaced with a P or F icon, representing Past and Future, respectively.
Time Warp Plates appear in the second zones of each stage. In present time, both past and future signs exist and are available to use. However, if the player is in the past or future, only one type of sign will exist. The player can either travel to the bad future (if the player has not destroyed the all the robot teleporters in the past or has not collected all the Time Stones), or the good future, if the player has collected all Time Stones from the Special Stages or destroyed all the robot teleporters in the past. However, if the player has destroyed all the robot teleporters, the player will automatically transport to the third Zone's stage in that level with the good future (or the bad future if the player has not destroyed the robot generator from either of the first two stages) where Time Warp Plates are not featured.
In Sonic Mania, a Time Warp Plate makes a cameo at the end of Stardust Speedway Zone Act 1, where it is used by Sonic, Tails, and Knuckles to warp to the Present version of Stardust Speedway for Act 2.