You can use a pseudo-element to insert that character before each list item:
ul {
list-style: none;
}
ul li:before {
content: '✓';
}
<ul>
<li>this is my text</li>
<li>this is my text</li>
<li>this is my text</li>
<li>this is my text</li>
<li>this is my text</li>
</ul>