@monorail Again, a multimeter can also identify the leads for you.
You're sure you can't tell which side is the anvil on them? We've never seen LEDs that you couldn't, though some you needed a microscope.
@monorail See this picture: https://i.stack.imgur.com/eHVnK.png
It's not 100% reliable but on most LEDs, the anvil is the negative side, and the post is positive.
You can always check the datasheet, too, but I find people don't often remember the exact part number, or even brand, of the LEDs to look it up.
@Rosemary yeah, these ones came in an arduino kit so i have no idea about part numbers or anything