Number plates can include a European Union symbol, Union flag, Scottish Saltire, Cross of St George or Red Dragon.
The law bans football crests or any other adornment or alteration to the licence plate because it hinders the effectiveness of roadside speed cameras and number plate recognition technology.
Acting Inspector Steve Hardy of the roads policing department, said: “Merseyside police prides itself on setting and maintaining the highest standards of professionalism.
“According to the regulations, registration plates are only permitted to display an acceptable international symbol or flag.