→Markers: Default set
You must type "dynmap" in square brackets on the first/top line of the sign, like this: <code>[dynmap]</code> (If your marker works, that won't be visible once the sign is placed.)
To put a marker in a set (such as NetherNetworkPortals or EndGatewayPortals), type <code>set:
[set_name ]</code> on another line.
By default, Dynmap icons look like signs on the map. To change that, type <code>icon:
[icon_name ]</code> on a third line. You can see the icon names [https://github.com/webbukkit/dynmap/wiki/Using-markers here] (scroll down a bit).
Anything else on the sign will be the text part (label) on the Dynmap. Labels cannot contain spaces and are case sensitive, but you can use underscores (_) instead of spaces. So something like this would be fine: <code>Cassolotl_JungleVillage</code>. If the label contains spaces it will not show up on the Dynmap.