There are two ways to separate prospect projects from production projects:

Probability value in Project's Dashboard
Soft booking (=tentative allocations)

Every project that is marked with a probability of 0-99% can be considered a prospect project.

You can use Silverbucket's filters to further differentiate these projects from actual production projects by using the project type filters.

The Projects > Listing and Projects > Allocations views show the probability of projects:

You can also use Silverbucket's Soft Booking functionality to indicate that the project is on prospect level.

Resourcing the project with tentative allocations indicates that the resourcing is not "set in stone" and changes are possible regarding that project.