Google Developers' YouTube channel has a video with step-by-step instructions on how to generate a valid signature from your customer key using Python.
Detailed explanations on the 5 steps you must follow to generate a valid digital signature are documented on Google Developer site with examples in Python, C#, Java, etc., but not in Adobe ColdFusion: http://goo.gl/iYLPi
I recently had to help a fellow Senior Developer with generating a valid digital signature using Adobe ColdFusion 9 to fetch a street view image associated with a coordinate point, and you can check out the steps involved and corresponding ColdFusion code snippet from my Google/Android Blogspot below.
Note: You can easily convert this snippet into a User-defined Function that accepts the coordinates as the input parameters and returns the digital signature in modified Binary64, that is safe to be passed as a URL parameter. Please make use of the function HMAC() that is available in Adobe ColdFusion 10 instead, if you're coding in ColdFusion 10: http://goo.gl/O1e2W
= google_mapapi_url & streetviewimage_
//Step 4: Convert the signature into something that can be passed within a URL.
//Step 5: Attach the signature to the URL parameter signature