If you download a sequence from Entrez, or open a sequence that is not in MacVector format, MacVector assigns a default appearance to any features on the sequence. For example, CDS features are shown as a blue arrow with a Helvetica 9 point font label. With the advent of ultra high resolution displays, you may find that the default font is a little too small to easily view. MacVector has a Default Symbols dialog that lets you control the appearance of every default symbol. To invoke this, choose the Options | Default Symbols… menu item (note in earlier versions you need to hold down the [option] key).
To change the font used for CDS features, select the Features tab, then click on the DNA CDS item in the list of feature types. Then you can click on the font button to select a preferred font using the system-wide font selection window. You can change the font for multiple features types at once by selecting multiple rows in the list using the or keys then selecting an appropriate font.
Note that with the current version of MacVector (15.1) you will need to close and then re-open sequence files for the change to take effect.