How do I show the binlog_format on a MySQL server?

To see the current binlog_format value:

mysql> show variables like 'binlog_format';
+---------------+-----------+
| Variable_name | Value     |
+---------------+-----------+
| binlog_format | STATEMENT |
+---------------+-----------+
1 row in set (0.00 sec)

To change it:

mysql> SET GLOBAL binlog_format = 'STATEMENT';
mysql> SET GLOBAL binlog_format = 'ROW';
mysql> SET GLOBAL binlog_format = 'MIXED';

Source: http://dev.mysql.com/doc/refman/5.1/en/binary-log-setting.html

Matt Healy answered the question on how to show/set the format from the mysql client (on a running server) with SET GLOBAL binlog_format = [STATEMENT|ROW|MIXED]

To set the value permanently, and assuming you have access to the my.cnf, add:

[mysqld]
...

binlog_format=XX

...

and then restart your server.