First of all, you should gain a rank by posting and making your activity higher. The higher that activity, the higher the rank you'll get. Then, you can join campaigns from the bounty sections of this forums. Try finding one that you think is good for you. Follow the registration instruction and mostly, when registering you'll be asked for you address and other information in order for your request to be accepted. Wait until you see your name on their spreadsheet. During those campaign, you should not try putting other campaign's signature and that will make them remove you from their campaign. Follow all the guidelines like 10post/week. You'll receive rewards based on the stakes ( which is based on how active you are during the campaign ). Then, after getting their tokens/coins, you can sell them for btc or eths or try to hold them for bigger value.
Edit:
Also, signatures are like advertisement. You are working for their campaign to get notice. You see signs from posts right? That's how they make their campaign to be noticed by other people. The more you post, the more you attract potential investor for their projects.
What should be the activity to participate in the subscription company?
a signature campaign, have a look in altcoins bounties there's alot of job waiting for you.