Maintain Runway Heading

[ZOOKER]

Tolka,
In fact thinking back, I am partially incorrect with the last statement.
The TWR controller at the airport in question could also apply the 'climb straight ahead, restriction' to traffic for separation against aircraft, (usually VFR/SVFR outbounds, which had taken off ahead of the 'restricted' aircraft), that were unknown to approach radar.
This was because, depending on the runway in use, the upwind half of the CTR was delegated to the tower. I believe the TWR controller had to have a valid procedural (ie non-radar) approach rating to provide this separation.