I have a homepage which has a script with a function which as well as other things, sets a cookie to true.

The homepage has an into and setting the cookie to true makes sure that the intro doesn’t display again if the user goes to another page and then returns to the homepage. However, if the user visits another site and then returns to the site I would like the intro to show again. At the moment it doesn’t. Is there any way to ensure this happens?

It could be done with a cookie however it’s a bit of a legal minefield at the moment for UK websites.
For those not familiar watch this:
Most webmasters are ignoring it but it’s an uneasy standoff and many eyes are watching what other .gov sites decide to do as many of them are not wholly complient either.

Would suggest using the ‘referer’ element, this will tell you what domain the visitor came from eg: Google,Bing, Yahoo etc or
the logic being in the referer value is anything other than your website then show the welcome message.

<!-- Hide script from old browsers : place inside the BODY tags
  if (document.referrer != '')
document.write('Hello and welcome blah,blah,blah ');
//-- Stop hiding script -->