{
    "fields": [
        "fire_hydrant/type"
    ],
    "geometry": [
        "point",
        "vertex"
    ],
    "tags": {
        "emergency": "fire_hydrant"
    },
    "name": "Fire Hydrant"
}

{
    "icon": "fire-station",
    "fields": [
        "fire_hydrant/type"
    ],
    "geometry": [
        "point",
        "vertex"
    ],
    "tags": {
        "emergency": "fire_hydrant"
    },
    "name": "Fire Hydrant"
}

Add fire-station icon for fire-hydrant
Add fire-station icon for fire-hydrant

Fire hydrants are for firemen anyway, and it help distinguish them from other no-icon point on the map. 

By the way, is there any plan to upgrade maki from version 0.5.0 to latest version 2.0.x? Is that OK if I migrate iD by updating icons' name or there is a particular reason to use maki 0.5.0?