IGLD 1955 - EPSG:5608

WKT

VERTCS["IGLD_1955", 
	VDATUM["International_Great_Lakes_Datum_1955"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["IGLD_1955", 
	VDATUM["International_Great_Lakes_Datum_1955"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "5608"]]

Data from @esri/proj-codes

{
  "wkid": 5608,
  "latestWkid": 5608,
  "macro": "PE_VCS_IGLD_1955",
  "name": "IGLD_1955",
  "wkt": "VERTCS[\"IGLD_1955\",VDATUM[\"International_Great_Lakes_Datum_1955\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"IGLD_1955\",VDATUM[\"International_Great_Lakes_Datum_1955\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"5608\"]]",
  "description": "IGLD 1955",
  "authority": "EPSG",
  "version": "6.15(9.3.0.0)",
  "deprecated": "no",
  "areaname": "North America - Great Lakes basin and St Lawrence Seaway",
  "extent": {
    "slat": 40.99,
    "nlat": 52.22,
    "llon": -93.17,
    "rlon": -54.75
  }
}