Not sure on either one.
Sobstad's logo, at least the one I remember, looked like this:
The one you've posted looks really familiar, but I can't place it. How old is the sail?
And, "in general" you can't tell the LP of a sail from the foot. The foot is usually longer than the LP.
The LP (the Luff Perpendicular). is the line that is perpendicular to the luff and goes through the clew.
To measure LP, hold a tape measure at the clew and measure to the closest point on the luff usually somewhere around a third of the way up the luff). That measurement is your LP. Divide that by your J measurement to get the "size" (125%, 150%, whatever).
On my boat, the LP on my everyday headsail is about 16.4' the J is 13.8' so my headsail is just under 120%