If Sonic and friends were ponies.
Name Pony type/species Cutie Mark
Sonic Earth Pony/Unicorn Power Sneakers (power-up), because even though he doesn't have his usual feet, his shoe is widely reconised as a symbol of his own speed.
Tails Pegasus Spanner, symbol for engineering.
Knuckles Earth Pony Fighting Glove, represent his strength.
Amy Rose Unicorn Piko Hammer, Her signature spells are hammer-spawn, heavy object levitation and teleporting to wherever Sonic is.
Shadow Earth Pony/Unicorn Hover Shoe, his own version of Sonic's cutie mark.
Rouge Pegasus Crystal, for her love of gems.
Dr. Eggman Diamond Dog None, diamond dogs don't have cutie marks. I figured being bigger than ponies and use of fore-arms to build stuff.
Silver Unicorn Psychokinesis symbol. In Sonic '06 there were marked out locations where Silver was able to use his powers to create paths from rubble, the symbols for these marks can be his cutie mark. Also Silver specializes in levitation spell.