I found this on the DEP's Website, As it states below the stickers are only good for one vehicle per pass.

http://www.ct.gov/dep/cwp/view.asp?a=2716&q=325090&depNav_GID=1650

Season Pass for State Parks
For the frequent park visitor, Connecticut offers a special season pass at a nominal fee. The pass allows unlimited vehicle access with the window sticker to any state park or recreation area that has a parking fee for no extra charge.
Season passes are:
Valid for one vehicle per pass;
Valid for the entire calendar year of issue;
Non-transferable to any other vehicle.

Season passes are not valid:
For admission to Dinosaur or Fort Trumbull State Park Exhibit Centers or tours of Gillette Castle, camping or special events with charges;
If an area is closed to the public for any reason;
For commercial use or on a commercial vehicle;
Unless adhered to the windshield (motorcycle operators may hand hold the pass) of a Connecticut registered vehicle.

Season passes cost $67 for Connecticut residents and $112 for Out-of State residents. They can be purchased online at the DEP Store, by mail or in person.
To purchase a season pass by mail, send a check for the appropriate amount (please add $2.50 for shipping and handling charges), payable to "Treasurer, State of Connecticut" to:
DEP Store
79 Elm Street
Hartford, CT 06106-5127

Your pass will be sent via first class mail with delivery confirmation to the address provided in your request.
The Season Pass for State Parks may be obtained in person at:
DEP Store
79 Elm Street, Hartford
Monday – Friday, 9:00 a.m.-3:30 p.m.
(860) 424-3555 DEP Eastern District Headquarters
209 Hebron Road, Marlborough
Monday – Friday, 8:00 a.m.-4:30 p.m.
(860) 295-9523
DEP Western District Headquarters
230 Plymouth Road, Harwinton
Monday – Friday, 9:00 a.m.-3:00 p.m.
(860) 485-0226 DEP Office of Boating
333 Ferry Road, Old Lyme
Monday – Friday, 9:00 a.m.-3:00 p.m.
(860) 434-8638
Sherwood Island State Park
Exit 18 off I-95, Westport
Monday – Friday, 9:00 a.m.-3:00 p.m.
(203) 226-6983

Passes are also available for purchase at State Park and Forest Recreation Area entrance stations during hours when parking fees are in effect. Visitors may show identification, buy a pass and use it immediately to enter the facility. Out of courtesy to the many visitors arriving simultaneously at larger parks during busy times such as weekend mornings, pass sales may be temporarily suspended.
If a windshield needs replacement or a stickered vehicle is sold during the recreation season, a replacement pass can be obtained upon presentation of the original pass or a recognizable portion thereof.