I see know now, well the answer would depend on how the site was hacked and the kind of site.

If it is a defacement then it will just look different with things people have already suggested.

However, if you are running a full web application ie with customers, database in the back end. It would be impossible to tell via the browser if the data of your customers has been exposed to a hacker/cracker (what ever the correct term is, you get my point). Depending how this was achived would depend on where the attack might show up, determining this kind of attack via the web logs or data base logs in some situations will also be near impossible aswell.

It would be possible to tell if the site has been attacked with a XSS vulnerability, but by veiwing the page with the malius code on you have just become a victum your self.

So sum that up, it would bepend on the kind of attack (and theres lots of them) to weather or not one could tell via the browser if you have been hacked.

SittingDuck