so i googled a little bit and found a digital gallery in new york public library archives

http://digitalgallery.nypl.org/nypldigital/dgkeysearchdetail.cfm?trg=1&strucID=715981&imageID=809574&total=1&num=0&word=police%20officer%201860&s=1&notword=&d=&c=&f=&k=1&lWord=&lField=&sScope=&sLevel=&sLabel=&sort=&imgs=20&pos=1&e=w

it's a 1863 depiction of the riots and front and center in one of the pictures is a police officer

Based on the image it also appears Scorsese's film "gangs of new york" (which ends during the riots) has a historically accurate police uniform in use as part of the plot (don't want to spoil the film but if you don't care just google it),