Look in the \BDMV\STREAM folder on the disk. If there is no single .m2ts file that is 20+ GB then it's pretty much certain that the disk is authored as seamless branching.
However, the converse is not true. Just because there is a 20+ GB .m2ts file does not mean there is no seamless branching. I have seen several titles that had a single large .m2ts file that was flanked before and after by one or more small .m2ts files.
Can you tell me why you want to know this? Perhaps there is another way around the issue.