Where is the Three digit key number for 1980 suzuki GS 550 motorcycle when the keys are lost. Thank You ED e mail Onthemoon769yahoo.com?

I lost my key for my 1980 Suzuki GS 550. Where is the digit key number for 1980 Suzuki GS 550 motorcycle as I lost the key? Thank you for your help, Ed from Smithtown NEW YORK