What is in the .SIG file? Is it an image? Then you could create an image object in each report and dynamically load the image information in the object. If it is a text file and you don't use report integration I think you will need to write an ELF to read the file context and return it from a function and call the function in each report. If the .sig file is static you could create a pagelayer with the information and use this in each report.