Some software programs put info about the program in the < head > information so you can view the source code to see if anything's there. I know FrontPage used to do that but that doesn't mean people won't remove it. I think CoffeeCup does the same. It depends on the software. But unless you are familiar with the templates a particular software program uses, then I don't know how you would know. For example, Site Build It! sites often use the same templates so there are identifiable attributes of many SBI! sites.
Also, it's important to note that a lot of sites are developed without software and they are hand coded.