Random characters after table name in FROM clause of SELECT query
As @dezso points out it's a table alias. You can also use as which makes it a bit more comprehendable:

SELECT * FROM client_messages as c


Why use an alias? It makes it easier to refer to the table. Assume the following query:

SELECT * 
FROM client_messages
JOIN client_address
    ON client_messages.client_id = client_address.client_id


Using table aliases:

SELECT * 
FROM client_messages as cm
JOIN client_address as ca
    ON cm.client_id = ca.client_id


so it's a bit shorter which is nice. When using self joins it becomes necessary to use aliases:

SELECT * 
FROM client_messages as cm1
JOIN client_messages as cm2
    ON cm1.x = cm2.y
WHERE cm1.... = ...


Otherwise there is no way to determine which one of the two tables one is referring to.

As a side-note, avoid using SELECT * other than for ad-hoc querying.