Sigaw is by Regal Films.
Other Pinoy DVDs that are in widescreen include:
Big Time (VideoFlick Productions)
Bikini Open (VideoFlick Productions)
Crying Ladies (Unitel)
Keka (Viva)
TXT (Regal Films)
Please note that all are non-anamorphic. All seem to be 1.85:1, except for Keka, which looks like it's 1.66:1. However, we have a thread on these forums by the film's director that states it was shot in a 1.85:1 aspect ratio. I think there may have been an error in the encoding, then.
It's possible the more recent Regal Films theatrical releases are all being done in widescreen. I'm not positive though - but TXT was widescreen, then all the trailers of Regal titles that came on the disc (Like Super Noypi & Shake Rattle & Roll 8, among others) were all in widescreen, as well. Hopefully someone who's purchased other Regal titles can add comments to this thread.