Remove the plus sign from year headings

I want to show a generic year heading and start with a partial year. The program adds "+" in front of the years. How can I remove the "+" sign?

Year headings showing Year +1, Year +2 and so on

Milestones doesn't add the plus sign. It comes from the heading's Prefix, which here was typed as "Year +". Change the prefix to just the word Year:

Click once on the date heading on the schedule. The toolbar changes to Current Object: Date Heading.
For the year level, pick Yearly: 1, 2, 3,...
In Prefix, type Year followed by a single space.

The headings now read Year 1, Year 2, Year 3 and so on. To begin counting at a different number, enter it in Start.