On my old mac laptop (which has a DVD drive) they included software to play DVDs and within the menus is an option to view disc specifics - somewhat unsurprisingly it reveals that many discs have more region codes than what is printed on the slip, typical combinations being 2 & 4 for PAL format or 1234567 (ie all-regions, the later numbers reserved for government use, I think).
The software also reveals if the disc is encoded in PAL format or NTSC, and some naughty companies such as Eureka now seem to use the horrible NTSC format for all of their DVD discs.