Issue with Signature in Template & the use if ISNOTBLANK

[drfuadj]

Hello, i need some help regarding this issue

Ive made a PDF template for my use case and there is a column for SIGNATURE.

In the SIGNATURE area in the template, if the SIGNATURE column is not empty, i want to put the 'Signature' , but if it is empty i want to put just the 'UserName' in the template. 
I've applied this expression in my PDF template:

<<IF(
ISNOTBLANK([_UserSign]),
[_UserSign],
[_UserNama]
)>>

The problem starts to occur when there signature column is empty and when it replace the area with the 'UserName' It creates a template looking like this:































This is the template expression in google doc:







Can anybody help me to search whats the issue with my expression or theres any other way to rectify this issue? Thanks