You could also do this for messages.
The sign-object will have the name "objSign" and your hero (the object that the player moves around) will be called "objLink". So then we could take the "Key-Press-Event" and take a preferable key to press if you want objLink to "read". What we put in as a code is:
if objLink.y=objSign.y+2
{
show_message("Hello, I'm a sign")
}
What happened, is that the objSign indicated that Link is standing on a y-position that is two pixels underneath the objSign. And if that is the case, then a message will pop up that reads "Hello, I'm a sign" (without the " though).(It's not always y+2, best try it yourself and insert different values until it works.)