This is a short convention.
Rule: Always display the label for the patient ID numbers
Whenever a patient identifier number (i.e. the data value) is displayed, a label must be attached.
Simple as that.
Do not only display in the patient banner the number without a label: 254 932 3022
Instead display: NHS No. 254 932 3022 or Clinic No. 392 932 3022 or. Tel. +254 932 3022
Further Examples of label placement above or below data value
254 932 3022
254 832 3022
1. If the patient identifier number is displayed in a table, the patient ID label can be displayed at the top of the column.
2. If a patient identifier number is displayed elsewhere, the label can be placed to the left, above, or below the data value provided that it is clear to the two are related. It probably could also be placed to the right.
3. It is important to style the label so that it is not as prominent as the data value.
4. Generally, a text label is used for the patient identifying the number. However, it is possible to imagine exceptions where an icon may be safely used instead. 
5. If the data value is not know, do not display a “?”, but an explanation such as “unknown”
The NHS CUI requires labels beside all the fields displayed in the patient banner.
This removes the possibility that a string of numbers on screen may be misinterpreted as something else.
 For instance, if the identifying number is a telephone number, it may be acceptable to use an icon of a phone. This still follows ITU-T E.123, provided the image looks similar to ITU-T E.121. (But, on the other hand “Tel.” is a rather short string and likely would fit where an image would fit also).