Aside from someone saying 'I like you, let's date', what little tells do you look for to see if there is a burgeoning interest there? I don't mean psychology like turning their knees towards you, but the things you have genuinely noticed and that have been successful tells in your life.
For me, it's them dropping things into conversation that you've mentioned in the past. Or casually asking if you're going to the same event as them.
Let's help each other out, or feed each other's delulu!