Image as initial value with condition

[Msidacappu]

Hi there,

My question is as follow, can you help?

1. I set a quotation form.
2. After save the file, it will generate a pdf file and I can print it and sign it. 
3. Now I want to add an additional function if I push a button "signed"， it will show a signature image that I would like to set it as a virtual column in " image" type. I set it as initial value but it shows always. I don't how to do. Anyway to set the condition? Sometimes I need it to be signed on the pdf and sometimes I need it not to be signed.