Comic fans spotted the mask of popular villain Deathstroke in a teaser trailer for the new CW drama, which is based on DC's Green Arrow series.
"That is most definitely the mask - I would encourage people to watch the show, particularly watch future episodes," Guggenheim said on The Outhousers podcast.
Asked if further DC characters would appear, he added: "I would say, watch very carefully and watch more than the pilot."
> Arrow star Stephen Amell: 'Black Canary could appear'
Guggenheim also revealed that the Arrow writing team have "plans" for what a second and third season would involve.
"We got picked up for 13 episodes," he explained. "The standard [network] order is pilot +12 and that's what we're writing towards.
"But we have plans for what episode 22 [the season finale] would be, what seasons two and three would be about, and with any luck, we get to tell all those stories."
> Smallville star Allison Mack on Arrow role: 'Never say never'
Watch a preview clip from Arrow below: