Following simple script can be used to check if there is any database in the current SQL instance is a part of the replication. This information can be pulled using SQL Server Management Studio, but if you have lots of databases it takes a long time to check manually.
SELECT @@SERVERNAME as [Server Name],
name as [Database name],
state_desc as [Status],
WHEN is_published=1 OR is_merge_published =1 OR is_distributor=1 OR is_subscribed=1 THEN 'Yes'
END AS [Is in replication ?]
WHERE database_id > 4
ORDER By name