Can a National Guard Officer transfer into active duty in Signal or Cyber series?

The only two options for active duty from the Guard/Reserves are:
(1) AGR - definitely has available slot for Signal officers but very difficult to be accepted as a 2LT. You will have better luck as a 1LT. It is even more difficult in the Guard. My advice would be to switch to the Reserves and then apply.
(2) Call to Active Duty program - this is regular active duty; the branches they will accept applications for change yearly so you have to read the MILPER announcements each FY. For FY15, Signal is not one of the branches listed, and they are only accepting applications for CPT and MAJ. Here is the URL: https://www.hrc.army.mil/officer/call%20to%20active%20duty%20program

I can tell you from experience. It's gonna be no I've been trying for almost a year to find a way to transfer. As of right now the only option for us is the " call to active duty " program and right now it is closed to all but Captain's. That could change next year. But the current milpar message says no LTs

1LT Christopher Sorge, from what I read in this Army Times article, members of the National Guard and the Army Reserve are specifically excluded from consideration for the Cyber Branch transfer.
http://www.armytimes.com/story/military/careers/army/officer/2015/04/16/army-cyber-voluntary-transfer-incentive-program/25811401/