TL;DR - “vid”.
When used in a Groovy DTH the ‘ocfDeviceType’ affects the icon used for a device when it isn’t explicitly defined in the ‘vid’.
The ‘vid’ is an identifier that seems to have been an acronym for ‘vendor ID’ - a code uniquely identifying a particular device belonging to an organisation or manufacturer - but is now a backcronym for the more community friendly ‘visualization ID’, or similar. It does the same job either way. It is used to identify a particular ‘device presentation’ (also known as a ‘presentation resource’ or ‘UI manifest’) which is a JSON file, about 100k big, that defines how the device should appear on the dashboard, detail pages and when building automations. It includes all the internationalization of texts which is why it is that kind of size.
The app will download the ‘vid’ and use that as the basic instructions for what appears. The actual design and rendering is performed by a ‘plugin’. It has been observed, often by me when I am particularly grumpy, that the plugin sometimes has a rather liberal interpretation of the instructions.
Anyway, to get the attribute you want on the dashboard tile you need to use a ‘vid’ that puts it there. That means copying one from a device handler that has the same capabilities and does what you want, or building one if you know how (it isn’t difficult, just not particularly common knowledge yet). Once you have a suitable tool installed - the CLI is particular helpful - you can get it done in five minutes.