はてなマーク、クエスチョンマークのアイコン

<span class="dli-question"></span>

.dli-question {
  display: inline-block;
  vertical-align: middle;
  color: #333;
  line-height: 1;
  position: relative;
  width: 0.15em;
  height: 0.24em;
  background: currentColor;
  border-radius: 0.075em 0 0.025em 0.025em;
}

.dli-question::before {
  content: '';
  position: absolute;
  left: 0.075em;
  bottom: calc(100% - 0.15em);
  width: 0.2em;
  height: 0.2em;
  border: 0.15em solid currentColor;
  border-left-color: transparent;
  border-radius: 50%;
  box-sizing: content-box;
  transform: translateX(-50%) rotate(-45deg);
}

.dli-question::after {
  content: '';
  position: absolute;
  top: calc(100% + 0.1em);
  left: 0;
  width: inherit;
  height: 0.15em;
  background: currentColor;
  border-radius: 50%;
}