DFW Controller described a operational deviation when failing to initiate a 'Call For Release' (CFR) on an IFR departure; noting weather distraction as a causal factor.

Narrative

While working Local West 1; Aircraft X was instructed to TIPH(taxi into position and hold) on Runway 18L at Zulu. The weather was LIFR and traffic was crossed down field while Aircraft X held in position awaiting an appropriate 'gap' from landing aircraft on Runway 18R. When an air carrier was on a 3 mile final to Runway 18R; I cleared Aircraft X for take off on the JACKY4 SID. After the aircraft became airborne; the Local Assist West 1 advised me that he had not called for a release from the Meacham North RADAR position and; at that time; 'Call for Release' (CFR) was required for westbound propeller aircraft. The Local Assist West 1 then coordinated with Meacham North RADAR to advise them of our mistake. Recommendation; due to heavy rain; strong winds; restricted routes; and LIFR conditions; I was consumed with concentrating on a higher-than-usual amount of tasks to ensure separation between aircraft and this was the primary reason that neither the Local Assist West 1 or I had remembered to call for release on Aircraft X. Part of this problem results from the fact that almost identical strip holders are placed in the Local Control bay--one of which says 'AUTO PROPS' (which indicates automatic releases) and the other says 'CFR PROPS'; which is what we had today. Because these strip holders are almost identical; when I'm busy it's difficult for me to recognize the difference. One of my crew members uses a technique which I plan to begin using immediately when we have automatic releases; he removes all strip holders which reference the propeller release status and only places the 'CFR PROPS' holder in front of himself when applicable; thereby recognizing; because of the mere presence of the 'PROP' strip holder; that he must CFR. I can see where this is a good operating practice and will be using it in the future to ensure avoiding this same mistake at a later date.