If you are - you could just put a tiny drop of Fray Block and them and it would stop as soon as it is dried.

If you are doing little letters they are often digitized without tie offs because it makes the little letters to bulky. if the letters are small enough I would not trim the little jumps if you can get away with it. I definitely would not trim the bobbin thread on any design unless it is fsl and needs to be seen on both sides. If the letters are larger then they should have the tie offs in between each letter and should not unravel. What are you using to produce your lettering? do you use your machine, software, or purchase the fonts.
Alice.