This thing is -270°C and is EVERYWHERE

The CMBR is NOT a signal. Try looking things up.
sig·nal1
/ˈsiɡnəl/
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noun
noun: signal; plural noun: signals

    1.
    a gesture, action, or sound that is used to convey information or instructions, typically by prearrangement between the parties concerned.
     2.
    an electrical impulse or radio wave transmitted or received.