There is a suspect ' in the expression.
Function FindLabel ( [LAT] )
Degrees = Int[LAT]
Minutes = ([LAT] - Degrees) * 60
Seconds = ((Minutes - Int(Minutes)) * 60)
FindLabel = Degrees & "° " & Int(Minutes) & " " & Seconds
In the above, i've removed the apostrophe that I thought was causing the error and that underscore. Excuse me if this is incorrect and there was an intended purpose for that?
Also, if your DD field is stored as text, this may not work as the expression looks for an integer in the Int() part of the script.
This label syntax may also require the If, Then, End If expression to make it complete...
If you can't get this to work, then I would recommend doing as suggested before, to create a new field. In this case a Text Field so that you can include the abbreviations and special characters of your coordinates in the field.
When the new text field is created, right click its header and go to Calculate Geometry. There is an option at the top for x or y centroids, and the bottom option is for the desired units, in this case, Lat and Long, and there is a full list of the examples and how they should appear in the final field. Also take note of the checkbox that asks if you would like to include the units abbreviations, click this to make it active.
If you need two fields in one label, then generate the x and y coordinates in your required geometry to separate fields than you can use a concatenation operator in the label expression to bring them together with the & key.
[Lat_X] & " " & [Lat_Y]
where the space inbetween the double apostrophes can be something like a dash or whatever you like.