I am not positive on this, and you don't see it as often as it used to always appear when there were only 2 or 3 major houses setting lines. First off, it does not matter at all which way it is listed, it is the same bet.
So if I'm understanding your question correctly, understand that at one time, some gambling houses would designate the home team as the last team listed and put the spread next to that team [Team A vs Team B (+21)...B is the home team, and they are the underdog] and would designate it by giving or taking away the points from that home team [Team A vs Team B (-21) ...B is the home team but they are now favored to win]. Anymore, you typically only see the favored team with the spread [Team A (-21) @ Team B].
The bottom line, it is the same betting line, and also should not be confused with a moneyline.