I don't think you can go wrong if positive is connected to pos on the battery and vice-versa. If the bike has pos earth or neg earth, the battery polarity remains the same.
If you are using one of the modern 'smart' chargers it will let you know if you've reversed the connections.
PS., A word of warning about those modern chargers; if the battery is totally flat they don't work. I assume they need to know the voltage and polarity of the battery connection before they can do their work.