There are no such restrictions for signatures that specifies the character type. So yeah! you can do that. But you should keep in mind that you should use the signature which is the same kind and you can write it multiple times. For example in case of banks or in case of competitive if your signature differs from the submitted one then it can be a problem. So you can choose whatever you want to do with your signature but remember the pattern of your signature for the official purposes.

**If you are using the signature for exams, then I would recommend you to use capital letters in your signature for the first letter of your First name and the first letter of the surname and keep the signature simple, because in case of exams students usually get nervous and if you do some pattern and out of nervousness the pattern can change. Although nowadays biometrics are available, but its better not to complicate for examination purpose.

I hope this answer helps. All the very best for your future endeavors!