There are two ways to programmatically verify that the underlying database is SQL Azure

1. By running the TSQL command: select @@version
if the underlying database is SQL Azure, the query will return something like:

“Microsoft SQL Azure (RTM) – 10.25.9640.0 Apr 2 2011 18:10:33 Copyright (c) Microsoft Corporation”

The returned value clearly states that the database is SQL Azure

2. By running the TSQL command: SELECT SERVERPROPERTY('EngineEdition')
if the underlying database is SQL Azure, the query will return value 5

Output of SELECT SERVERPROPERTY('EngineEdition') as value

To know more about serverproperty. go here