When browsing explorer.acinq.co, I noticed some nodes display an icon image in front of their name. How can I configure such an icon for my own node with LND?
You can assign an alias to your node. The als is what is being depicted in node explorers. It is a regular utf8 string. Nowerdays there are a lot of icons as characters in utf8 encoded strings. For example ⚡. So in lnd and in clightning (apparently both have the same Syntax) you could add the following line to your config file:
alias=⚡my node name with icons⚡
After restarting your node and waiting until the gossip protocol has propagated your new alias you will be able to see it on node explorers.