I have only ever used Photoshop for pieces of artwork and I now need to create high-res in-store signage for digital print. I am not sure which programme would be better to use for this: InDesign or Illustrator? Most artwork will already exist, I may just need to change prices or add in text/banners where appropriate. Can someone suggest which would be the better programme for me to receive further training on?
For single page layouts like signage or posters that's a difficult call. Either program will work.
Illustrator has much more sophisticated drawing tools and soome 3-D capabilities that InDesign lacks, but ID has more sophisticated text handling and will do multiple pages more easily, if you think you might also need that capability. Persoanlly, I use ID for layout, assembling elements previously produced in Photoshop and Illustrator as appropriate, and doing the text elements in ID.
As Peter says, for single page layouts, either will be okay, but keep in mind that InDesign CS6 has alternate layout capabilities that may come in handy if this signage needs to be created for many different sizes.