For each individual area (Silver Lake, Waterfront, etc.), there are two different possibilities for a Signature Takedown. Performing a unique Signature Takedown will yield a photograph for your album. Performing all 20 Signature Takedowns will unlock the Oval Circuit Racer. You may do this in any World Tour or Single event.

Gone Fishin': Send an opponent off the cliff near the Silver Lake trailer park.
Home Wrecker: Force an opponent into a motorhome.
Pillar Driller: Force an opponent into a Downtown elevated railway support.
Hit the Split: Force an opponent into the median at the Downtown tunnel entrance.
Tram Ram: Force an opponent into a Waterfront trolley.
Truck Torpedo: Force an opponent into a truck carrying a boat.
Euro Tram Ram: Force an opponent into a Winter City trolley.
Snowed Under: Force an opponent into a snowplow.
Avalanche!: Send an opponent off either of the Alpine suspension bridges.
Paid the Price!: Force an opponent into a tollbooth.
Riviera Roustabout: Force an opponent into the monument at the Riviera traffic circle.
Berth Trauma: Send an opponent into the Riviera marina.
Grapes of Wrath: Force an opponent into a wine van.
Gate Crasher: Force an opponent into the wall of the Vineyard's main gate.
Catch the Tour Bus: Score a Bus Takedown on Paradise Island.
Rumble in the Jungle: Score a Takedown on the Paradise Island dirt road.
Market-Stalled: Score a Takedown in the Golden City marketplace.
Tuk Under: Force an opponent into a Tuk Tuk.
Tunnel of Shove: Score a Wall Takedown in the Dockside Tunnel.
Shipwreck: Score a Takedown in the Dockside wharf.