How do I sign an application for the TI-83 Plus? What program do I use? Thanks!

Use spasm and app.inc. That page should also describe how to set it up Just be sure to #include "app.inc" at the top of your source file.

What do you mean by signing?

If you're asking specifically about signing applications compiled with Axe (and provided that you're on a Windows computer), you already have the preferred tool: rabbitsign. It is distributed with Axe in the Tools\Application Signing directory. The aptly named "Drag App Over Me.bat" file can be used to sign unsigned applications compiled by Axe and transferred to your computer without using the command line.

For signing assembly programs, if the assembler can handle it for you like Mateo suggested, that's probably best. Or you can use rabbitsign, though you may have to experiment with the command line options for it to work properly with your setup.

I was thinking about signing the program created for Emu8x

EDIT:
I am trying to convert the emulator.hex file to an application. I can't find the ti 83 plus flash debugger

You would need to use rabbitsign then.

thanks, I'll try this