We had two signature cocktails and I think it was worth it. We had a BOC bar so they were charged per drink. We provided light up ice cubes and rings and named one the Bridezilla for me and the other was the Rowdy Reptile (after UF gator basketball b/c DH is alum).
I was going to do a signature drink, but I was afraid it would rack up my bar bill. We are doing BOC and I worried that having a signature drink might make people more likely to drink an expensive drink over a cheaper one.
I think it's a fun idea though, if your budget allows for it!
We had 2 signature drinks. The blue drink was a Grey Goose pear based drink, served up, garnished with a strawberry and the red was a 10 cane rum, served on the rocks and garnished w/ blueberries. (Oh I wish I had tried them- they were apparently awesome!)