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This really depends on the project you are joining. That is why it's good to read the instructions for each project before joining just as you have said earlier. Some projects do allow you to join their signature campaign as a junior member. I can see you are now a junior member, it's great and I'm really happy for you as you are gradually ranking up. With that you can now take part in some signature campaign. But always read the instructions as a guide for any campaign.