The concept of a "second mortgage" is signed as: SECOND LOAN
It is also okay to fingerspell M-O-R-T-G-A-G-E. I suggest you spell it the first couple of times it comes up in a conversation and pair it with the LOAN (or BORROW) sign. Then, if the only type of loan you are discussing is a "mortgage" you can drop the fingerspelling of "mortgage" and just sign LOAN. However, if several different types of loans are being discussed you can either continue spelling out the word "mortgage" or you can use a combination of the signs HOUSE and LOAN.
See: MORTGAGEAlso see: LOAN
The concept of "percent" in this phrase just uses the normal "percent" sign.
See: PERCENT
To sign 125 you just sign 100 followed by 25. Some people will sign 100 as 1X other people will sign it as 1C. Your local ASL instructor may try to tell you that it is one way or the other. If so, sign it their way and get the grade you want then go do your own research in the Deaf Community: write "125%" on a blank card and then approach 10 native Deaf people individually (not together) and ask them how they would sign that concept. Personally if it is near the beginning of the conversation or if I'm feeling formal and wanting to articulate clearly (if I'm signing to an audience vs an individual) I'll do the 1C version. If I'm relaxed, signing to a few people (rather than a large audience) and have been discussing numbers for a while I tend to do the 1X version.
If you "do" research whether 125 is signed more often in your locale as 1x25 or as 1C25 -- have some fun with it by trying a card that states: "I THINK 125 PEOPLE GO WEEKLY" Or try, "I NEED 125 DOLLARS" -- and notice if doing the sign "THINK" and/or the sign "NEED" (which use "index finger shapes) just before signing "100" causes people to do the 1X version more often. Then try a card that states: "I BUY 125 CUPS" and see if the shape of the signs BUY and CUPS influence individuals to sign 100 as "1C" more often.
SECOND: You will see the word "second" signed various ways. It is common to use the "L" hand version of "second" as in "second-hand" for concepts such as "a used or second-hand car" or a "step" parent (a secondary parent). Thus it is fine to sign the "L"-hand version of SECOND in the phrase "2nd mortgage." But there is another good way to sign SECOND (in the phrase "second mortgage") and that is to use the palm-back-2-handshape (which incorporates a small quick twist. This is the version that I recommend you use since it is a standard "ordinal" and fits the concept of a "second mortgage" being the next mortgage after the "first mortgage."
See SECOND
Notes: