Can I sign it with something else?
Sign it with any bitcoin address you have ready there. Just be mindful that any changes you want to make (pay now and return collateral, change payment date, change return address, etc.), I would need a signed message from the address that you will use to sign the message. This is for your own safety in case of hacking or unauthorized cases.
I am Caffe1ne4Life . Today is Saturday, 15 July 2017.
I certify that I have read and agreed to all the terms and conditions of this loan.
My receiving address: 1s3n2LxV2xKVBfGWD7G9cQvGww74fDipQ
Repayment amount: 0.5361
Repayment date: Saturday, 22 July 2017
Repayment address: 1thrEeYgPMr9c5sjHnpdJpJfjKbgwG4Rz
1DKM5xxbM1eqq67mi8QGhzQkEBTngJaWZo
H+pGriW5jSkGmTL5Z2pC1m5f9TNhBajA5ubjbuqVmFgUZMEoHGBHlhi4cA1+DjYYmijVud/gINbYhXwuy7zlq6Y=