A champion is identified by behaviour, not by tone. These three tests are cheap to apply and considerably more informative than any number of positive meetings.
The access test
Do they introduce you to colleagues, including people you could not reach on your own? Access is the resource a champion controls, and someone unwilling to spend it is telling you something about how far they will go.
The information test
Do they tell you things you could not have discovered yourself, including inconvenient ones: internal opposition, a competing project, a budget that is tighter than implied? Sharing the awkward facts is what distinguishes an ally from a polite host.
The action test
Do they do something without being asked? Circulating a document, arranging a meeting, raising the topic in a review. Unprompted action is the strongest single signal available, because it costs them something and nobody made them do it.