If you edit the language table under the Member tab you can change the text next to fields. So, in this case if you want to add the word "Optional" next to the Product Title and the Order Title fields. Just follow the below instructions...
Click on the Members Tab and Select Member Language Content. Then chose the language table on the left that you want to edit. Then select the "define content" button on the right and then you will be presented a page where you can select the page where you want to edit the value.
To add "Optional" to the Product Title field select the page link as identified in the below image.
Then type in the word "Optional".
Click the save button.
Then to add "Optional" to the Order Title field, select the page link as seen in the below image.
And then add "Optional" as below
And then save your way out of the whole Member Language routine.