Im going to take a different tone to the existing answers.
Go for it.
Seriously, you stated that your company policy doesn't explicitly forbid it, so there is no real company-side risk for this. Be sensible about it too, don't get stalker-ish, but expressing interest is worth it. Jobs change and percieved unprofessional behavior is forgotten, your life however is important.
Other answers state that office romances seldomly end well, and that may very well be the case. But ask yourself this: Are you willing to take the risk that it might not go so well? If yes, you should definately go for it. Especially since your company policy explicitly does not forbid this.