You could try:

CREATE TRIGGER [dbo].[PostDBRestore]

ON [msdb].[dbo].[restorehistory]

FOR INSERT

AS

SET NOCOUNT ON

DECLARE @DBName AS VARCHAR(256)

DECLARE @User AS VARCHAR(256)

SELECT @DBName = destination_database_name

, @User = user_name

FROM INSERTED

IF @DBName = 'YourDB' ....

SET NOCOUNT OFF