Time Warp Plate
From Sonic Retro
Time Warp Plates or Time Warp signs were first introduced in Sonic CD. They appear similar to Lamp Posts, and are the basic means of transport between different time periods.
In the future versions of the levels, 'Past' Plates appear, whereas 'Future' Plates are strewn about the past versions. The present versions have some of each. Upon touching a plate, it will spin around, and a 'Past' or 'Future' icon will appear next to Sonic's life icon, indicating which kind was touched. To use it, run as fast as you can, and a warping effect will appear behind Sonic. After a few seconds of maintained speed, the icon in the corner will begin to flash. Continue running for a few more seconds and Sonic will travel through time. If you stop running while the icon is flashing, however, you will lose its power. This is a good way to prevent yourself from accidentally traveling through time.
A 'Future' Plate reappears in Sonic Mania as part of the transition between Act 1 (which takes place in the past) and Act 2 (which takes place in the present) of Stardust Speedway Zone.