You need to register your ATV with a local Louisiana OMV office. The documentation required is the same as basic titling requirements. You'll need a completed vehicle application form, manufacturer's statement of origin or title, and an itemized invoice or bill of sale, and proof of insurance. The registration fee is $3 per year for four years. You will also be issued an ORV decal upon registration for 1987 and later ATV models.
Check out these Longstreet, LA ATV/OHV resources: