Custom Heads

There are 2 ways you can give custom textured heads:

Using name of player to receive a custom head

items:
    player_head:
        id: PLAYER_HEAD
        texture_name: "{player}"
        slot: 7
        name: "<#85a16a>Your Profile %player_name%!"
        lore:
        - "&7Are you currently online? %player_online%!"
        itemflags:
        - "placeable"
        triggers:
        - "join"
        enabled_worlds:
        - "world"

You can either use a player name (example: "Notch", "Technoblade") OR you can use the inbuilt placeholder for heads {player} which gives player's head

Using texture values to receive a custom head

items:
    player_head:
        id: PLAYER_HEAD
        texture_value: "texture_value"
        slot: 7
        name: "<#85a16a>Your Profile %player_name%!"
        lore:
        - "&7Are you currently online? %player_online%!"
        itemflags:
        - "placeable"
        triggers:
        - "join"
        enabled_worlds:
        - "world"

You will have to get texture value (NOT SIGNATURE) to use this! Here are some websites to find some heads you can use

Gallery | MineSkinMineSkinOrg

Minecraft Heads