There are many unrelated Johnstone families. Some have mottoes and some do not.
One Johnstone family motto is 'nunquam non paratus' which means "never unprepared." Some families translate that as "Proper Preparation Prevents Poor Performance" or P5.
"Never unprepared," also "Nunquam Non Paratus" or "Nunqum Non Paratus," usually the motto of an empire or empire's military that is preparing for war, or so it seems from a quick google search. Also, the Johnston (Johnstone and multiple other spellings) family crest motto.
The Syer family motto is "Bear and Forbear".
R Family Vacations's motto is 'RFamilyhome'.
The motto of Focus on the Family is 'Helping Families Thrive'.
The Whitney family motto is translated to "Willing and able".
The motto of Arnold family is 'Ut vivas vigla'.
The motto of the Ballew family is With pure life and heart.
Holy Family University's motto is 'I am bound by my responsibilities'.
Kings Family Restaurants's motto is 'At Kings, you rule.'.
Metropolitan Family Services's motto is 'Amazing Strength'.
The motto of Holy Family University is 'Teneor votis'.
nil admirari. To be surprised at nothing.