A group of people is sitting at a large table and using paint brushes to form characters on white paper.
The people are making a welcome home sign.
Sentence 1 does not specify what type of sign, a welcome home sign, is being made.
Just because a group of people is sitting at a large table and using paint brushes to form characters on white paper doesn't imply that they are making welcome home sign.
not all people using pain brushes are making a welcome home sign