Are you talking about the code itself or the clue that a poster is going to be a nightmare to help? In either case, aside from what you mention, a lack of commenting is a good clue. I'm glad you mentioned the variable names. Well defined methods and variable names make it so much easier, as well as PROPER indentation so you can immediately find blocks of code. Any good program of that length should have some comments at the top and/or a README which explains exactly what the program does, what assumptions the programmer makes, what input is needed, the output to expect, etc. Good error messages and good prompts when asking for input are essential. If I make a mistake when entering input, I want the program to catch it, tell me what I did wrong, and give me another chance to enter the correct input.
If your question is dealing with good/bad Daniweb posts and predicting what will be a nightmare to help on, I'd say that displaying effort is the big one. I'm willing to wade through a lot of bad coding practices if I sense effort on the poster's part.
A good thread on a forum has a paragraph or so with an English description of what the problem is, what has been tried, what input is expected, the ACTUAL output, and the DESIRED output, including a SHORT sample input FILE if needed. Preferably it is a short, but COMPLETE program that we can simply copy and paste and compile/run for ourselves. We can't do that, often, if there is a function that is posted that relies on functions or variables that AREN'T posted. At the same time, don't post 30,000 lines of code and a 50,000 line input file. It's vital that people understand that other people are not familiar with their code and they therefore must explain explicitly what their intent is. I think we all fall into that trap (I certainly do). We're familiar with our own code since we wrote it, so it's "obvious" to us and we forget that others can't read our minds.
BAD postings are verbatim copy and pastes of the initial assignment with not a single word from the OP him/herself. That goes straight to the "effort" issue. Salem used to post a link of the good/bad ways to pose a question that I had bookmarked and have subsequently lost. I think it should be pinned to the top of the forums since it's so well written.
Long winded, but that's my two cents.