In my dreams, I dont seem to have a common dream sign. The only possible dream sign that I seem to have is that most of my dreams take place at night. The thing is that most of my dreams aren’t outside. The other times I have gained lucidity is by randomly doing an RC in my dream. Is there another way I can find a dream sign?
Do you have a DJ here?
If you do, I’ll try and look through it for you.
Sometimes it needs an outsider opinion to find common dream signs.
I have trouble finding them in my dreams also. 
Edit: I just looked through your DJ and I couldn’t find any common links between the symbols in your lucid experiences, sorry. 
I would suggest from now on writing a list of all the objects in your dreams, both prominent and not so important. Colours are also very important. I don’t usually see a lot of bright red IRL but it was repeated a lot in my previous nights dreams. Also think about your friends and family, not so much as symbols, but their reaction to certain situations. My DC friends and family act different than IRL so I usually try and do a quick DC whenever I feel like they are doing something abnormal.
I do keep a DJ, just not here. I only post my lucid dreams online. The rest I record in a notebook.
Yeah, it can be tricky… keeping a DJ and going through it sometimes helps. You might have to have a bunch of dreams in it to find a dreamsign, I don’t know how long you’ve kept your DJ…
And remember also that dreamsigns don’t have to be objects or places or whatever… They can also be reactions like Ethanescence said, strong emotions, or even feelings.
One of my dreamsigns, for example, is getting extremely angry and start destroying things, for no or little reason. 
I’ve become lucid with that asking “hey, why am I so angry all of a sudden?” Another is a feeling of weekness or weight all over my body. In one dream I felt my legs very weak. I was almost falling to the ground. So I did TWO RC’s and neither worked. I was still almost sure I was dreaming though…
I find that when I think a lot about a particular thing, I tend to dream about it a lot. perhaps you could just create a dream sign by thinking about something a ton.
Well now that I go through my journal, I noticed that my mom does a lot of things that she normally woukd not do in WL. Like she will be driving in the freeway, even though in WL she doesnt. In my dreams she also sometimes listens to heavy metal music. Si I think I found a dream sign