There is little leftover data related to riding the skateboard. The skateboard is developed enough that it is specified to which surface is skateable. In the gta3.img file, the animation file for the skateboard exists.
On the other hand, the skateboard does exist as a fully functional weapon except in the PS2 version, where only the HUD icon remains. However, it is normally disabled and cannot be found anywhere. It can be enabled by swapping it with an existing melee weapon in the game files.
There was also a skater pedestrian who was dropped from Grand Theft Auto: San Andreas. Although his true purpose is officially unknown, he almost certainly would have interacted with the skateboard, and likely would have dropped it upon death. It's very probable that he was cut when the skateboard was cut. No model or texture for this pedestrian exist in the game files anymore, but his leftover voice lines remain, and can even be coded to be spoken by another pedestrian.
The skateboarder pedestrian is introduced in Grand Theft Auto IV, and can often spawn with a backpack. Texture files for this backpack reveal textures for a skateboard, suggesting it was once again removed; given Grand Theft Auto IV's limited activities in comparison to San Andreas, it likely would have only been seen as an unusable prop here.
- data\american.gxt>STRAP2>STP2_34>To use the skateboard pick it up and select it from the weapons inventory items. Press ~k~~PED_ANSWER_PHONE~ whilst over it to pick it up if your inventory is full.
- data\american.gxt>STRAP2>STP2_38>To use the skateboard, select the it from your weapons inventory. Use the movement controls to steer the skateboard. Tapping ~k~~PED_SPRINT~ helps you pick up speed and ~k~~PED_JUMPING~ makes you jump.