Placement restrictions and visual indicators for custom entities

[JAetherwing]

Hello everyone,

I want to create an entity that can only be placed next to rails, similar to a rail signal. Furthermore, it should display a similar or the same visual indicator as a rail signal when you hold it in the cursor. However, I don't want to use a rail signal itself as the base prototype, as I neither want my entity to require one tile space to the next signal, nor should it split rail blocks.
As I'm quite new to modding and still getting used to the API, I'd appreciate some hints how I can create something like this.

Thanks in advance!