Why?  ICE is a federal police force and as such it is entirely proper for them to identify themselves as police officers.  To police is
a :  to supervise the operation, execution, or administration of to prevent or detect and prosecute violations of rules and regulations
b :  to exercise such supervision over the policies and activities of

ICE polices the federal rules and regulations regarding immigration.  Words have meanings and definitions regardless of what Mayor Hancock thinks or believes.  And, like ICE, I'm not all that concerned what you, Mayor Hancock or any other individual who supports the practice of illegal immigration thinks or believes the word police means.