You can test to see if a layout variable has been set using perch_layout_has().

The following code checks to see if the Layout Variable “title” has been set. If it has then the contents of that variable is output, if not a predefined string is output. You can use this to create a fallback state if a page does not populate the title variable.

    if (perch_layout_has('title')) {
        echo "Welcome to my site!";