Good question! 
In short: only if you know it has a custom icon on Twitter.
The long version: currently we take merchant icons from Twitter, so if you know they have a Twitter account with a custom icon, then please do flag it up (and ideally include their @handle). In the long term, we’ll probably expand that to include Facebook/Instagram/the wider web. But for now, if it’s a tiny cornershop/restaurant, they may well not have any custom logo so we’ll stick with our general category icons.
Hope that makes sense?