The security thread is incorporated in the banknote when the paper is manufactured. The vertical security thread is a darker tone line that is visible when held up to the light. The windowed security thread comes to the surface at regular intervals so that its metallic sheen may be seen. The complete thread is only visible when held up to the light.
2003 Issue
This issue has a windowed security thread which for added security was widened from 1.4mm to 1.5mm. When viewed under ultra violet light the thread glows blue. When viewed against the light, text in the thread of a genuine banknote will read "BELIZE" followed by an inverted “BELIZE”.
1998 Issue
This issue has a windowed security thread. When viewed against the light, the text in a genuine $20, $50 and $100 banknote will read “Belize” followed by the denomination of the banknote.
1990 Issue
The vertical security thread in the 1990 issue illuminates when viewed under ultraviolet light.