I think it's pretty clear from the responses that we're guessing off of your pictures. Take it to a reputable shop or frame builder for assessment before riding. It could be just tape residue, rust from clamps, or cracked tubes. I'd hate to tell you what it is if I didn't have it in my own two hands.
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If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.