When Oliver and Thea are meeting at the coffee shop called "The Grind and Jolt" Thea's coffee mug reads CC Jitters, the name of the coffee shop predominately featured in The Flash.
When Oliver comes up behind Nyssa in the safe house, the Scimitar she pulls on him is a rubber prop sword.
When Arrow is fighting Nyssa after rescuing Thea. When he does a spin kick and it misses Nyssa, his hood flies off backwards and is back on in the next shot.