Community is signed exactly like city: take both slightly curved flat hands, then have them touch at the fingertips while facing opposite directions. Switch both hands' positions while twisting them back and forth, releasing and touching the fingertips a couple of times. This is also the same sign for village and town.
Teach your baby or toddler the community sign when you are driving by or dropping off something at the community center. Teach it as well when you encounter 'community' in your child's cartoons or story book.
Teach your child this sign in the context of community center visits or story book mentions.