encode, in code

Encode or encode ( one word ) means to convert or translate into code; to convert into symbols meant to convey meaning secretly, to another person, or to a computer--
He learned to encode messages in the army during the war; he still works for the government.
You'll need a computer engineer to encode that for the web page.

In code or in code ( two words ) describes something written in a cypher or code, something that has to be deciphered by another person who knows the code; or something written using computer code--
This looks like nonsense; I think it's in code.
I can't understand this email; some of the words are in code.

Now that you know that, you can say--
"This doesn't look like it's in code; but a clever spy may have used this ad to encode a secret message."

Note--"decode" means to convert something that is written in code into an understandable message--
The security agency spent weeks trying to decode the message.